[RICK LAKE]

charlandk Kevin there are a couple of silly people on here trying to compare to different styles of rearends. You have a couple of pictures of race cars. You can't compare a Nascar rearend to a FFR spec racer. Nascar rearends have floating rearends and alot bigger bearings in the housings.
Short course on rearends, either rearends have solid axles that are held in place my bearing plates or have "C" clips holding the axle into the housing.
IRS have there own setup with on a jag rearend of bearings and plates on stub shafts. Some IRS have clips to hold the stub shafts to the center section. as far are rearend torque, this is silly to me. Thrust angle of the car is the only thing I would worry about. You want the car to go straight. Thrust angle should be as close to "0" as possible if the car is balanced. If something is loose or worn out in the rearend, this may cause a torque issue. 2 different size tires on dirt cars may use this term more.
Getting back to your car, T-56 if this is stock, you are at the limits without not doing a blueprinting of the trans with installing better gears( stronger material) better syncro's. The New t6060 is up to the power you want. If you are going with a 3.73 or higher, the trans you need has the low first gear of no more than 2.40. This will give you the double overdrive with a .80's something and then a .60's something. This will give you the best of both worlds. If you are going to drive this hard, a differential cooler may be needed on long cruises or some kind of duct work to remove the hot air around the rearend. If a IRS posi car is setup right, it will out handle a solid axle car because the tires can remain more flatter on the road than a solid axle going around a turn. What posi units are you looking at? I run a locker in mine, it's a little clunky but the car hooks and runs good with both tires work about even in the rearend. IRS car also lets you better setup a car with independant suspension or each tire that is not controlled with a solid axle. If you are drag racing, Solid axle wins hands down, to many extra ujoints, CV joints than can be broken under extreme abuse. Rick L.