As long as an external manifold gets plumbed to the main oil gallery with a big enough hose or hard pipe, and the oil pump has sufficient volume, I doubt if whether it's inside of outside the block will make much difference. Dry sump oil systems keep NASCAR engines alive at 9K RPM or so. "You can't do that" usually means "Nobody's done it yet!"
LOL!
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!