If you want an "original-appearing" system, just gut out an old mechanical pump and install a sheet metal baffle where the diaphragm used to be. Then run the line from the electric pump through the check valves in the fake pump housing. The biggest risk of running electric pump output through an unmodified mechanical pump is the possibility of gas leakage into the crankcase from a ruptured diaphragm. Wire the electric pump circuit through an oil pressure sensing safety switch.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!