Unless you have considerable experience with engine swaps and setting up driveline and suspension systems, I would not recommend using a BBC in this little truck. A well-built SBC will move it along in fine style. Here are 109 dyno-tested SBC combinations built with static compression ratios that will be compatible with pump gas. Take a look through them and you'll begin to see what works with what..... Ryan's Stroker Combo Page (108 and up!)
If I lived close to you, I'd bring my sledgehammer over to your place and smash those 624 heads so that nobody would ever make the mistake of using them again.