A tundra is huge, and the leafs in back are not the way I would want to go. Personally, if I was going to build a stretch 40 with a modern drivetrain, I would be looking for a rolled GX470. You get a V8, coils, longer, but not too wide, ATRAC, etc. You can buy a custom stretch body from aqualu to fit the frame, and then try to swap the harness, booster, pedals, pretty much everything from the donor on over. If you are dead set on a solid axle, then it shouldn't be too bad at that point, but I think I would run IFS for a bit to try it out. I'm pretty sure an aluminum 40 with no top would be substantially lighter than the GX, which should make for a pretty stout drivetrain.
Some fun figures:
FJ cru 4,290lbs
Comparing the GX to the FJ, you can see that all that insulation, heavy seats, and gadgetry add a whooping 500lbs! I would guess and alu 40 might drop that curb weight somewhere around 3,800 lbs, which would make it a ROCKET.
1978 13BT-40, 70 series mechanicals
1966 FJ45 lwb stock
2003 100 stock
1974V8J40, 1992FJ80, 1985FJ60, 1971FJ55, 1978FJ40, 1974FJ40, 1997 LX450 all long gone.
Last edited by OilHammer; 07-26-2013 at 11:36 AM.