Aside from the obvious (350 CID vs 393 CID), it would really be a final expense decision. If the adapter pieces and SBC cost less than rebuilding the Cleveland, then you've got to weigh the lower HP to the cheaper cost. I've done the 393 thing with my 351 Windsor, but also had the AFR 225 (?) CFM heads and nice cam, and it was a monster (great rod length to stroke ratio using the longer rods from the kit). Make sure the ZF transaxle is up to the task of the added torque, and review some of this transaxle's issues on the web. It's a great transaxle, but be informed and prepared, so that it will provide trouble-free service.