Take a look at this, it looks like the whole lifter galley would have to fill with oil before it drains over the cam. I had issues with oil pressure at the end of a pass when hitting the brakes the pressure would fluctuate. I included pictures of a stock block and the dart shp.

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Here's the dart

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Okay, so a few things here:

1)notice the "hump" in the production block. That's the main oil galley. If you look at the dart block it has huge oil holes where that is. These were likely changed for "priority main" oiling.
2)The oil should drain through the above mentioned slots.
3)As much as I hate to say it, I wouldn't be a fan of the Dart style setup. I can see it being good for cam life on a flat tappet setup (more oil to the lobes) but having a negative effect on windage and possibly mean that more oil control is plausible in cases of a roller.

Where historically this sort of thing has been a problem is pickup depth, oil pan control and possibly pump cavitation. Looking at the last pic on your thread you seem to have a decent pan, I'm guessing a bolt on pickup with checked clearance? They can get "sucked" into the bottom of the pan. Oil selection is another potential issue, and I'd give consideration to one of the "plates" they make that goes between the oil pump and the pickup to keep oil in the pan.

 

Alot of people install oil screens on those oil drainbacks. I'm not quite sure it really matters on a street car but circle tracks or any extended time high rpm I believe screens would help reduce some windage and regain oil control.

In OP's case though I'd look at oil control in the pan if the pressure fluctutations appear when braking at the end of a run. The valley return holes sit pretty low. You do get oil from the lifters in the valley but being a priority main oil block you usually get the most bleed at the crank, then the cam and last the heads.

 

Here's what I have for an oil pump pickup, it's roughly 1/4" off the floor of the pan

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What does baffling look like

I was under the impression those screens were to keep valvetrain shrapnel from the top end out in case there were problems up top.

That said, you have a very valid point on oil control in the pan. It makes sense that there's enough braking force to pull oil away from the pickup.

 

Inside the pan it has a trapdoor just forward of the oil pickup in the sump to prevent oil from going forward. I think I'm going to try and add an extra 1/2 quart of oil when I get it running again

 

Yeah quite often it can be the oil level. These leaky and sweaty old engine designs lose more oil than we think sometimes. If you have a windage tray be careful not over filling. Well that goes in any case. In your shoes I'd drain the oil, measure how much I drained, know how much oil the pan takes and fill accordingly. If the level is correct you might have a stuck trapdoor. I've even seen where some trapdoor pans are installed engine upside down, trapdoor open and when you turn the engine right side up the trapdoor is stuck in open position.