Help chosing a performance engine for my car

Hi i am new to the whole performance scene and was wondering if anyone could give me some advice. I have a 70 EL Camino (was my dads) and was considering putting a 383 in place of the old tired 350 thats in there now. I was checking out websites for performance engines and one stood out to me. Has anyone used this place before? Any feedback would be greatly appreciated.

thanks in advance

This is the link to there website www.promarperformanceengines.com (http://www.promarperformanceengines.com)