At least the 292 has a high-volume pump available, so dropping the rate to the mains isn't a big deal.
The lifter gallery wouldn't be my first choice, though. It's (almost) system pressure, but each tappet is a leak so the pressure goes down with the distance from the feed. You can compensate by using progressive squirt sizes, but IDK how to tell how much the rate will decay across the 12.
Are you thinking of tapping the inner wall of each tappet bore directly?
The ideal spot for this is really as high up on the wall that the skirt stops just above, which requires major plumbing (like sinking a tube into the block casting). If you don't need the squirter to actually protrude from the wall, it can be as high as (perhaps) 1/8" below the oil ring @ BDC.
