I doubt that this is a GM engine. The Holden small block V8 was an all Australian designed and manufactured cast-iron 90 degree pushrod OHV engine, manufactured in the capacities of 4.2 L (253 CID), 5.0 L (308 CID), later destroked to 304 CID), and 5.7 L (348 CID - never actually built as a 'production' motor). First introduced in 1969, finally ceasing production in 1999, it powered a variety of Holden vehicles including the Kingswood, Monaro, Torana and Commodore, and proved to be a popular and successful powerplant in Australian motorsport (especially Touring cars). Much of the design is from Ford and one good example is the fuel pump design.
Use a block off plate and then an electric fuel pump to solve the problem you have. Pretty easy.