Anji, not a good idea to enlarge those holes. Their part of a metering system. If too big more oil will go up there instead of the oil tank and could overwhelm the scavenge side of the pump.
These are not actual figures but just an example. Imagine there's 100 ml/minute of oil going in the feed side and the scavenge side can pump 120ml/minute at the same revs (that's why there's bubbles in the return to tank oil). Now say the scavenge pumps 90 to the tank and 10 to the rockers so in reality there's 110ml going in but that's OK as the scavenge can do 120ml. With larger holes say 70 to the tank and 30 to the rockers means there's 130 going in which is 10 more than the pump can handle. In theory the sump will slowly fill and the tank empty. As I said this is just theory but could happen. By increasing the hole from 3/64 to 1/16 will increase the area of the hole by 77% which is a sh!t load.
If the oil line is clear the banjos are clear and the shafts are clear there will be oil up there. With the motor running loosen one of the banjo bolts, oil should emerge. Tighten that one and loosen the other, more oil emerges. Tighten both. Remove tappet covers, start motor, finger over return pipe in tank, should be able to see oil dribbling out the rockers. If not the pump can't give enough pressure to get through the bolt holes. Time to look at the pump. Lap the end plate on a piece of glass with wet & dry (400 grit) till the gear wear marks are gone.
Well that just about wore the print off my one typing finger!
Cheers