Read an article on Mechanical fuel injection in Hot Rod Magazine. If you find 3 hash marks on a fuel pump Hilborn put them there because the pump isn't rebuildable. There are 120 different intake variations for Sm Blk Chevy. Send Hilborn the serial number & they'll tell you everything about your piece. Tell you what it fits, application, port runner, butterfly size, & whatever other parts are needed to make it work properly. Other manufacturers keep similar records. 