[68 TT]

Lots of questions in one post.

The 2-wd T-400 has a longer output shaft than the 4x4 version so the transfer case adapter on the NP205 is too short to work with it. You can have the output shaft swapped for the 4x4 version or find a 4x4 T-400. You could make a custom spacer to use the 2-wd trans in the 4x4 but it would cost more than getting a 4x4 trans would so it isn't worth it plus then you would have to get custom length driveshafts built.

The T-400 / NP205 combo is fairly common in 3/4 & 1-tons.

The mount on the transmission goes away when you remove the tail shaft housing so the trans will bolt up to the transfer case adapter. There may be holes in the frame already to just bolt the crossmember right in place or you may have to drill some new holes. From your description it sounds like you have a car or 2-wd truck application T-400. I would put it up for sale and find a 4x4 version to use in your build instead.

With 35" tires, 500 hp and going drag racing in mind I would go with a set of Dana 60's front & rear. What gears you use depends upon what RPM you want to push the engine to. Assuming 6000 rpm shifts, 5000 lbs and 500 flywheel HP running 5.13 gears with 35" tires you would go through the traps a little over 4900 rpm. 4.88 gears would drop it down to ~4700 rpm and 4.56 gears would put it at ~4400 rpm.

I would go with the 4.56 gears as you would still have a decent cruise RPM at 70 mph on the freeway at about 3100 RPM. I run 5.13's & 32" tires and it sucks without overdrive.

My track won't let trucks with selectable 4-wd systems that can go into 2-wd run in 4x4 mode. You might want to check with your local track before you build a 4x4 drag truck.