Best carb to get for a carb conversion....?

Holley street Avenger. I think they make a 600 cfm avenger. Has all the hookups and emissions ports aaand, even has the AOD tv bracket already in place. Nice vacuum secondary carb for good milage and throttle response.

Get a fresh one. You want to know that for whatever reason it is not working after the conversion, the issue is not the carb. You dont want to debug a carb as well as the conversion.

edit
I was wrong.....

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7973561400&category=33550

It's a 570. Look at it this way, nascar uses 390cfm's. It enough for them and the cfm formula for carb selection says:

CID x max RPM / 3456 = CFM

302X5000/3456 = 436 CFM
302x6000/3456 = 524 CFM

The 302s dont make any power in the high 6000+ ranges unless you've cammed it and changed the motor.

With that 570 avenger vacuum secondary, the throttle response will be insane. Here's what I run

http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSC/0-80540-1.html

I think the mechanical secondaries are hurting my performance a bit.