I was actually just looking at the galley numbers out in the shop.
Here's the real stomach-turner. If you look at the stock system (all values in sq inches):
Right galley area: .2215
Total passages feeding off right galley: .441
That is not including any of the right galley lifter bore losses, which would be significant.
It also ignores the fact that the galley is fed by an oil passage that is under .196.
If you were to feed oil to the left galley and use it to feed the lifters and #1 main, the numbers get better:
Left galley .2215
Total feed-off: .098
Right galley .2215
Total feed-off .298
Those values are all 'estimates' as I have no way of knowing the lifter bore losses, especially for the right side. Because the left side is fed through a .250 passage, I did flip that back and forth as the left galley lifter losses. That's as close as I can get.
With my planned mods (thus far), I would be at:
Right galley .2215
Total feed-off .234
Left galley .2215
Total feed-off .087
Those numbers DO account for all lifter bore losses accurately so they are more of an improvement than it appears. They are also based on my enlarging the main feed passages to .281" which further inflates the feed-off number.
The benefit of a front/rear feed would be in the ability of the pump to maintain a stable pressure. The double feed would not make the pressure any higher but it would flow more (if there was demand) and would be more stable, i.e. less sensitive to sudden swings in demand.
Whether single or double fed, the system would remain restricted by the single feed passage coming off the pump (let's call it 1/2 dia). But the galleys act as a manifold, a 'storage' vessel for pressure and volume.
If you made a 2" diameter galley, the engine would take longer to build oil pressure when you started it. But once it did, you'd have a very stable system.