----The oil pump gasket is not only just a gasket designed to prevent oil leakage between the Oil pump body and the pump base but also acts as a shim/spacer for the oil pump gears clearance settings. The oil pump base needs the thickness of the gasket to give it the correct clearance from the rotating gears otherwise the pump gears will bind on the base plate and cause subsequent & catastrophic damage to your engine. .
--- It is always the best idea, to check the correctness and free rotation of the gears prior to fitting the front timing cover and distributor. Final checks such as this are always very important when it comes to building reliable engines of all power levels.