Thanks guys, your input is much appreciated!
GP - I'm pretty sure it's not hanging up on the clutch pack splines because the teeth are all worn off. I can spin the brake hub independently of the clutch pack and hear / see it rattling round inside (note to self: order new clutch pack parts from General Gear...). It's as if the casing is stuck at the very front adjacent the pivot shaft. I verified via the parts diagram plus visual inspection that I do have all the bolts out. One thing I did notice is that the pivot shaft cap that bolts on the underside has a dowel that locates into the pivot shaft. I'm pretty sure that there isn't a corresponding one on top between the shaft and the casing.

Gary - the casing is loose at the back and moves in and out maybe 1/8. The front does not move at all (as if a bolt were still installed but unless my eyeballs are deceiving me, I have them all out. On the track frames, I'll leave them alone until either they start to move and break up or I find replacements. I figure if I try to weld patches on them, that'll weaken what's left. It'll have to be a driveway cruiser until I get some decent frames. I have to believe that I can find a 5U above 13273 parts machine at some point. I presume the corresponding 4U has the same track frames. I can't imagine any reason they'd be different.

Mike, well I do like fixing things : ) You're not too shabby yourself with some of those units you brought back to life. That unit you fixed up with Joe (are you sure he's not the former leader of JoJoZep and Falcons?) Good plan on the magazine, I will send the ladies in the office a request.

I think it's the dowel too as I sprayed the gasket line and the dowel and adjacent bolt holes with PB Blaster and then wiggled the housing and they all demonstrated fluid movement except the dowel. I'll get the gas axe out tonight and see if a heat will get it moving on the dowel. Hi Jeff, all bolts are definitely out so we're in good shape there. Interestingly the bolts looked like hardware store specials as they look galvanized - silver in color - and the part # in the book is for regular black bolts. I also took a look at the splines and teeth in the clutch pack and the teeth are all wasted away, along with big grooves worn into the brake hub

I think I was wrong about it being the dowels. I put a bit of pressure on the casing using a bottle jack and the steering clutch no longer was able to rattle around in the hub. So I worked the jack on and off a few times and the casing kept coming further. I then used a bar underneath the sprocket to wiggle the casing up and down while simultaneously leaning on a crowbar inserted in the gap between the casing and the transmission housing and eventually it came free. I decided that it was ultimately helpful that the clutch plate teeth had rusted out because if they were solid, I'm not sure how easy it would have been to get the casing off. Anyway, it's off now, the bolts holding each hub (outer and inner) are removed and I'll get the puller on them tomorrow. I've decided that given the condition of the parts, I'll just get all new from General Gear (hubs, plates, springs, pins, keepers, bellows seal, and bearing). Tossing up whether to replace all the bearings while I'm in there - it would mean some more disassembly of the final but I suppose if I'm in it this far.... : ) The one I should really examine hard is the bevel gear bearings because those would be a pain to change out I'm assuming.
Some pictures - I figure that the previous owner one day lost drive on the left side because of those grooves worn in the hub and then he just parked it up. I could spin that left sprocket by hand. Note also the brake band rusted right out so that'll get a new one too. Starting to get excited because once this side is bolted back together, I'll be able to move it around under its own steam and steer using the left side. Turn it around and then deal with the right hand side, which has a swollen pack.

It's a bit of a basket case all right so it's just as well that I enjoy fixing these old tractors : ) I cleaned off the track frames and it looked like it had ash or lime or something rock hard like that in there. Shame that the previous owner(s) didn't know or care to clean the undercarriage.
The next challenge is that the banjo bolt holding the lube tube on to the release bearing bracket is rounded off and of course it's not that accessible for a welder or such. I might need to blow it off with the gas axe if I can't get it to move, but first I'll weld a piece of rod to it short enough to be able to turn all the way around without hitting the transmission housing then heat and hit.
Haven't thought yet about reinstallation apart from reading up a bit on it last night. Probably will heat the hubs in the oven, tap them on, tighten, and call it a day.
Turns out I also have a 3J in parts at the moment although I haven't touched the backend apart from filling the steering compartments up with oil : )

Didn't need to weld anything as I remembered that I had some pipe wrenches which, with a bit of heat, removed the banjo bolt. Next are the two bolts that hold the thrust bearing cage to the yoke. Can someone confirm that the threads are in the yoke and not the cage? I think the cage is supposed to be able to rotate a little relative to the yoke. Of course mine is rusted solid.
Also, given the amount of wear on the outer brake hub where the plates wore through the splines, is my inner hub also likely to be that worn? I'm trying to decide whether to save it or not, because with my Harbor Freight hydraulic puller cranked up as much as I can bear, and with heat on the hub, it won't pop off even with some radial tapping with the 10# hammer. I've heated it a couple of times and left it overnight but it's not moving. So I'm trying to decide whether to cut a slice up the inside of the hub so it'll give a bit more.
Advice?

I also got my mag back in the post today from Mainely Magnetos and it looks brand new and is hot. So I'll be able to return the Eisemann back to the 3J's pony. Some helpful chap relieved me of my tree saw so I picked up another - never ends....: