If you're gonna bolt a 305 together because of limited budget, o.k., but don't spend one red cent trying to port those turd heads. Run 'em like they are with a good valve job until you can afford some decent heads. Figure you exact compression ratio before you ever try to pick a cam. If you don't know how to figure it, see this paper I wrote....
http://streetmachinesoftablerock.com...opic.php?t=124

Here's a dyno-proven combination....
http://www.goingfaster.com/spo/325_h...chevrolet.html