You could run a 3.5" or 4" single exhaust system.
http://www.mufflex-performance.com/fbody_1.html
Larry, I would think you could use the 86 pump. I have an all Pontiac 79, and a Chevy powered 89, and the pumps appear to be the same on both - just different brackets and pulleys. But if the 73 pump is easier to work with, give it a try. It is probably a standard vs. metric issue.
And don't forget subframe connectors - I consider them a necessity on any performance thirdgen!