LA heads on a magnum block

You're swapping from a system that hits the shafts with pressurized oil for about 10° of 360° degrees of cam rotation to a metered flow of oil for 360° of rotation. Personally - I'd do everything I could not to have to run LA heads on a Magnum short - but if a customer told that's what they want I'd go the pushrod route before I did anything else. That's a lot more oil spraying up there than any shaft delivery system. The factory shaft system is virtually a splash system anyway given the allowed volume.