All depends on how much money you want to spend on your engine and how nice you want it to look (relative) and how much gain in performance you want to get.
I got my 12 volt GM HEI, dual exhaust manifold, carbs , T5 transmission with adapter kit and dual intake manifold from Langdon's Stovebolt Engine Co.
http://www.stoveboltengineco.com/acartpro/
I would order a special ground cam or Edgy aluminum head from Earl Edgerton. Vintage Power wagon is also a source for modified cams.
I would also recommend intakes exhausts and rebuilt overdrives from: Asche George Jr
(814) 354-2621
1693 Fertigs Rd, Venus, PA 16364-1823
I bought my engine rebuild parts from:
Terrill Machine
Route 2, Box 61
De Leon, Texas 76444
254-893-2610
There are other after market suppliers in the forum listings that you could also check out.