I've got a rebuilt 343 w flat tops, holley intake 401 ported 58cc heads w/triple valve springs little better than 401 stock cam rhodes lifters. cRank drilled to fit auto or manual trans. Would take 401 or 390 parts on trade + $$.
Used to be that you could replace the spring in the oil pump to increase the oil pressure. the spring regulates the oil pressure=stiffer spring rate. This amc book i have says you can increase your oil pressure by machining off .003 to .005 thou off the bottom of your aluminum housing.(where your "plate bolts on.) To know how much you can shave off is to plastigage how much clearance you have between the gear and the plate. Anyways.....do you want to sell your 390?$$