I once saw a chevette with a blown 355 in it ,Bad News Man the guy couldn't get it to go straight . If you can get 1 H.P. per cubic inch you wouldn't be doing to bad with the 283 but the compression is going to be lower with the big chambered 350 heads . Milling the heads will help,use headers 1 1/2 -1 5/8 max not to much exhaust either 2 1/8-2 1/4 max. 280- 300 H.P. is possible on a budget. A engine builder once told me 100 C.F.M. for every 1,000 R.P.M.'s on 350 chevy i t's pretty close and pretty simple ,it work's .If all you have is the 620 C.F.M ., try it , it's only a little bit oversized but should work if your going to rev it.