Deas, You have my description correct. There is probably 4 or 5 inches of frame in front of the idlers. The tracks aren't excessively loose in my opinion. The springs being tired may be an issue. I guess the question is how long should they be when the track is adjusted? The distance between the coils right now is probably about 1/4" if I remember right. Another thing I will get a picture of.
A larger idler wheel does sound like the way to go.
If someone knows what models, and years that fit, please let me know. New is probably too expensive, for this old machine.

Thanks

Hi, R2D2.
Here are a couple of photos of recoil springs in reasonably good condition. The first two I'm guessing would be similar to yours::

 

And some more just for chuckles:

   

 

Hope they help.

Just my 0.02.

Hi Deas, In the 1st photo there is room in front of the idler on the frame. There is similar room on my machine. There is a rod on top of the frame that runs through a yoke that guides the idler arms. In the picture that rod shows a couple inches of travel before the yoke is pushed out of the rod. On my machine that same rod has no travel left outside the yoke. The end is about even with the edge of the yoke. That is the area I thought a spacer could possibly be inserted after the nut is loosened to provide the slack.
I remember there is dirt on the spring. It seems like it was more compressed than the one in the 1st photo, but I'll need to clean it off to look closer and get a picture. Thanks, I really appreciate your thoughts on this.

Hi, R2D2.
If you can take some photos and post them here, it would help folks here to have a better idea of what to tell you about your rig.

Just my 0.02.

Yes, I was planning to do that, but I won't be back at the dozer until sometime next week. I'll take pictures of everything I can think of thats relevant.

Hi, R2D2.
As and when you can. I'm not sure whether I'm 'retired' or 'retarded', but I have some time to spare.

Just my 0.02.

our d4 has the disc type front idlers so that must have been a later development.

i would also check the wear amount on the track chain itself as these may have worn too far.
remember a bit of wear everywhere adds up to a lot.