FWIW, you got good advice here, but my input would be that the lifters with the flat ground in them, Crower Camsavers, are no benefit if you don't have pressure to the lifters, and potentially little benefit other than a touch of added insurance.
In theory, hot oil could drain a bit through there from the valley, it likely will do little for cam break in when oil is thick, and will likely provide so little oil even when hot when compared to what the crank throws. My hunch is drainback it wouldn't make any significant difference.
When you put that slot under pressure, different story (maybe) because although as I said, I am going to use them to give us every bit of insurance we can with this little mellow street Pontiac (280H-ish hyd cam, 10:1, 4 speed, stocker), that slot will be on the trailing edge of the lobe far more than the leading edge as the lifter spins, unlike an EDM hole that is located where the load is.
Brent will steer you right, but if you want to go aggressive on a race car, I'd go solid roller. I am a solid flat tappet guy too, but if you want to go quick and steep in an undrilled 427 block, if you can't drill, I'd go solid roller
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 445 cid FE, headers, RPM intake, 1000 HP series Holley, 4 speed