The way I see it, the longer the wheelbase, the better. 118 was about all I could get out of this tank. If you guys can get 124-130, awesome. The front axle can go wherever you want it, but the problem is in the rear. The quickchange hangs so low in the back, you can only stretch it out so far, before you can't get the cover off. I don't remember the track widths off the top of my head, but when I get back into the shop next week, I will measure them.
As far as caster goes, I like a lot (I run a front engine dragster with 25 degrees). I ended up with 18 on the tank, because I had to modify the split wishbones. They were set up for about 7 degrees, so I had to cut them apart, change the angle and re-weld them. I didn't want to take off too much material, so I stopped at 18.