Saw your thread on classracer.com too.

I believe you would have to get a c-clip eliminator for the 8 1/4" rear because I'm pretty sure they are illegal (unsafe) under NHRA rules.

As mentioned by others, a Dana 60 won't slow you down much, if any at all. Most people I've heard commenting on the change didn't lose anything and some claimed to be slightly faster! It is a more efficient rear than the 8 3/4" (Takes less HP/torque to turn.) because of the location of the pinion contact relative to the ring gear. A Chevy 12 & 10 bolt are more efficient and a Ford 9" is the worst, but of course they aren't legal. 81/4" might be pretty efficient, but weaker, minimal ratio choices and fewer aftermarket parts. Overall weight is really irrelevant because the car has to be run at a minimum weight with driver anyway. Plus, the weight is in the back where it will do the most good. When you start replacing internal parts with aftermarket pieces that are lighter, the weight difference between a Dana 60 and 8 3/4" shrinks - (i.e.:lightened ring gear & spool, ) because the Dana 60 parts weigh more to begin with. Axles can be drilled and lightened in the flange area in either type. You also don't need a back-brace for a Dana 60 like you should have for an 8 3/4", bringing the 2 even closer in weight. Only down sides I see is that you need to get the gear ratio correct the first time and swapping gears is not as easy. Easier to get PRO gears for a Dana 60 as well. But either can have cryo and/or Superfinishing done for longer life.

I believe in the benefits of a Dana 60 enough to have installed one in my K/SA Aspen Wagon.with a 360 at a minimum weight of 3,927 starting out in the 12's! Got one for my trusty Dart Sport @ 3,530 minimum weight for IHRA Stock capable of low 11's. But that one hasn't been installed yet and don't know if I'll be out with either one anyway.

Get a Dana 60. It will be better and cheaper in the long run.