Engine Lube Question - fresh rebuild

depends on if theres a guide for the cam chain in the cover. some are like that, some arent. if you dont have to worry about it(guide), maybe try it for a few seconds to see what happens. its not going to shoot oil everywhere at 4 psi i wouldnt think.
i dont think oil has to go anywhere other than the cams as far as the oiling requirements go....the cam chain is going to pick some of the return oil and some at the bottom of the crank
have a look at an external top end oiler kit, im pretty sure they just put oil to the cams...

The compressed air thing might work...

comes up through outer studs in block,thn though oil passages in head(area above cylinder head nuts with plugs driven into them)then through holes under cam bearings as far as i know.running the old style motor without valve cover is no big deal ,but you might want to prop bike straight up and down so oil doesnt puddleto one side of head;)