This seems to be a common issue with the vast majority of people building their cars
While the aftermarket accessory drive setups are top notch quality, are more "compact" in their design, I have found over the years that there is a greater number of car builders that don't have approx $2300-$3000 in the build budget, to shell out just on a accessory drive kit
Again, the aftermarket kits are very nice parts, but they do have their draw backs
ie. alot of us building these cars are doing so with the intentions of driving the hell out of them, putting many miles on them and going on road trips with them, not just a "track car" or show car, getting there on the back of a trailer.
The main benefit to using the GM accessory drive kits, is that if you are on the road with your better half and unfortunately breakdown due to any type of part failure (ie waterpump, alternator, p/s pump, tensioner, etc) you can easily go to any of the local auto parts stores, buy a replacement parts, and be back on the road
With the aftermarket kits, most use specific designed water pumps, alternators, tensioners and p/s pumps all that may or may not be readily available "on the shelf" without it being a special order and a few days out to get the part in to your location
We are going to be using this GM kit and a/c compressor relocation bracket on SpiffaV8's 67' Camaro build that I am working on
http://www.jegs.com/i/Chevrolet-Perf...57325/10002/-1
http://www.kwikperf.com/lsx_ac.html
search on Ebay or other sites and you can easily find "new take off" Corvette balancers approx $75 and water pumps for $100 from crate engines
that puts you into a complete GM accessory drive (Sanden compressor comes with A/C system ordered) for approx $900+ (approx $700 if no a/c)
here is a pic of my personal 68' Camaro w/ Corvette access drive kit
hope this helps,
Jeff