Plenty of things you CAN do. Every little bit helps. Bush the lifter bores. Block the left galley (yes, even with the lifters bushed). Plumb oil to the main galley into both ends. Take the head oiling away from the cam bearings. Restrict oil to the cam bearings and the heads. Hand fit the pump to the main cap. Enlarge pickup to reduce restriction. Relieve/enlarge all oil passages.

The object of the exercise is to get maximum constant oil onto the crank and rods and minimize the amount of oil being sprayed around doing little or nothing. Most of this only requires time, some hardware and information.