You can check out Kwik Performance as well. They have a few different options and you usually can choose which accessory drive you are starting with be it truck, camaro/gto, or corvette length.
http://www.kwikperf.com/
I'm running a GTO accessory drive on my '69 Camaro and using a Kwik Performance A/C bracket.
I should mention that Wayne at Kwik Performance is extremely helpful and always seems happy to talk to a guy.
I had to cut out a section of the sub frame to fit my alternator in the factory GTO/Fbody position. The GTO alternator is a bit smaller than the Fbody one, which helps.
There should be some pictures of the operation in my build thread in my signature.
Also, I think Holley is making some accessory drive brackets now but I haven't seen them in person.