i am going to be changing a mec. pump in the spring. [not holding proper pressure] and was trying to find out if they can be rebuilt. or what replacement pump is suitable. one other question is a big block gm pump such as a holley the same or is the drive arm diffrent.

Mercury - Mercruiser V-8 Fuel Pump Assembly 861677T

Just put 2 on mine.

The fuel pump that mounts and drives from the sea pump uses a different drive arm than a standard BBC pump. Check with CP Performance for a replacement.
Eddie