So you have a 2 bolt main block ande want to add hp. How much hp do you plan on with this engine? If you are worried about the 2 bolt caps you can switch the three center caps with a set of Howards billet steel 4 bolt splayed caps. Howards Cams Extreme Billet Main Caps H350S - SummitRacing.com
. As for building a 350 engine I wouldn't. For the same amount of money you can build a 383 stroker engine with more hp and torque. Have your block checked out by your machine shop. Shop around for a 383 cid rotating assembly. Scat Engine Rotating Assemblies 1-90350BE - SummitRacing.com
If you want good heads look at AFR, Dart, Brodix aluminum heads. The heads produce the power so don't cheap out.