The pump will never miss it if the gasket isn't included in the assembly. I've run plenty of oil pumps without a gasket between the pump housing and the base. Just be sure there's a little vertical clearance between the gears and the base plate to allow for expansion due to heat. If you choose to make a gasket, I'd suggest using a piece of soft aluminum like a Coke can rather than paper. You really don't want a blowout with full oil pressure against the gasket.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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