COE OK, all you engineering types, drive shaft length?

Hi all, still in the planning stages for my '47 Chevy coe, the plans are for an LS-1 and 4L60E mid mounted with most of the engine under the seat. My question is this: What would be the minimum drive shaft length most would feel comfortable running? The truck will be pick-up style with load rated rear suspension capable of towing around 6000# (that's the plan at least). My Cobra (kit) has a 8" center to center drive shaft and I have no issues with it being that short, but I only need about 5" total travel. I have limiting straps for downward movement. On the truck I think I'll need more like 8". I need a little trig help here. I know the relative angle of the drive shaft from output shaft to rear end in static condition will here matter here, but I'm not sure what that will be at this point. Try to wrap your collective brains around this question and let me know what you think.

 

OK, so I've been playing with the numbers here and I've come up with 12.8" to maintain the same angles as the Cobra. That being said I think I will need at lease 5 inches of compression, is that going to be enough? then I would have 3" of drop, is that going to be enough? The Cobra is a light car at 2300#. The truck should be in the 4500# to 5500# range, sound about right? Of course it will have a higher spring rate. I'm just not sure if 5" of compression will be enough.
I think I will mount the engine level as the truck will be lowered a bit. The Vette and I think the F body both sit level so I don't see an issue there. Keeping the engine level also gives me a little more clearance under the seat, as I will build a raised floor at the back of the cab. Using the LS-1 intake and the F body oil pan makes the engine a bit shorter. I can also flip the intake 180 degrees and use a low mount alternator for more clearance. Lots of planning going on here. I will start the cab mods in April.
Thanks, Fast

 

Typically the driveshaft should only slide in/out of the trans about 1/2" as your rear end moves up and down. The shorter the driveshaft, the more in/out movement (***uming the same up and down travel of the rear end).

If your driveshaft is straight in line with the rear end, while at rest, then your travel is 4" up, 4" down.

There are other factors involved that effect the movement, like the arc of the rear end, but basically a 12.5" driveshaft length will move the shaft in/out 0.6" , again so long as it is in line with the trans at rest. I'd call that acceptable.