You can make pretty good power out of a rebuilt 5.7 with just a cam and heads. As James said it would be the easiest way to go. The wiring would go from the donor to yours as a whole but I’m not certain about guages ignition dummy lights ac and the like here’s an article on line I found several
http://forums.superchevy.com/gm-hig...need-swap-help-please-57-vortec-to-53-vortec/
http://forums.superchevy.com/gm-hig...need-swap-help-please-57-vortec-to-53-vortec/