D2 5U Blade?

First off, I wouldn't mess around putting a blade on a D2!
I would find a D2 with a blade already mounted as you also want the large front idlers which balances the operation of the blade. Buying the parts to do the job will run into some money plus finding all the little pieces to do it right. You want a CAT 44 hydraulic system so that you have live hydraulics with the brush guard plus larger front idlers and longer rail/tracks
As far as "Tinker Toy", tell your brother to look for Youtube videos from tractorjeff in Wisconsin. He seems to get alot of work done with a D2!
drujinin

A D2 will pretty much do anything it's bigger brothers can do. .it just takes a bit longer and sometimes, a bit more thought before ya start.

In my opinion, a decent D4 is about the ideal size for most stuff, plus I don't have to hire someone with a semi and flatbed trailer to move it. I've got an old Ford 5 yard dump truck and a 20k tandem trailer that I use. Makes a bit of a load for the old critter but I'm never in that much of a hurry anyway 😆

Not sure of your location, but I do have a 1951 D2 5U for parts with a 44 pump and 2A cat angle blade assembly-- Was going to put this on my 48, but decided to leave the smaller pump and factory rear hydraulics on it. I am in Central Minnesota- Trator has the solid front idlers, has bad crankshaft according to previous owner-- u can contact me at 320-980-5777 if you wish-