Are you aware that some of the transition engines had a fuel pump mounting, a pushrod hole but no lobe on the cam for a pump? Did you check your cam for a lobe?

Do you have roller lifters? Then, you probably do not have a fuel pump lobe on the cam...even if you can bolt a pump onto the block. On later engines (like Vortecs), the boss is there but the pushrod hole is not.

Take your pump off and hold the pushrod up against the cam while someone slowly rotates the engine. Such will tell if you have a pump lobe.

Chevy fuel pump pushrods are 5.75" long if my memory is correct.

mike in tucson