Overdrive transmission swap questions....need some input

I think the 518 into a cbody will be easier as cross member / torsion bars are not welded to body as with everything else the pressure switch setup those and others have to control trans is worth every penny think seemless operation, I'm moving switches, levers, buttons all day in my truck I don't need that on the weekend on the way to a car cruise with a automatic. I think cable for the kickdown my bro in law has a lokar setup on his cuda, I don't know why it was on there when he got car and seems to work well lots of adjustment. My biggest hangup with the 518 is that .69 is tall great if you have 4.10 in rear but it just has no pull in a theoretical world if you have 200 ftlbs coming into od gearset regular 440 at 2000 rpm and you multiply that by .69 you get 138ftlbs into the driveshaft which turns into 405 with 2.94 or 445 with 3.23 compared to lets say 400 ftlbs at 3000 rpm times 2.94=1176ftlbs or times 3.23= 1292ftlbs you can change numbers but I think I am fairly close of course friction knocks some off but it starts to become clear that the od with the hwy gears of yesteryear don't jive. Again I am not saying don't do it just have to look at whole package because od hunting is a crappy drive in out in out. You can always change gear later and have a better guess as to what gear to go with.

I have been looking for a c body that some a-hole stole BB from to put a modern pu/van 5.9 efi od trans in. I don't want to take one apart but rather than it go to crusher I'm looking but a lot of these a-holes want what they paid for a running car that aint happening.