Before bushing the lifter bores on a factory Mopar big block, the oil area is very large. It is formed by the intersection of the oil galley and the lifter bore on the edge of the lifter bore.

I would estimate the opening is roughly .25" x .50", maybe larger.
That is an area of .125 sqin. So a round hole of the same area would be 0.40" dia

1993 Daytona, 5.50 at 130mph (1/8) 1.19 sixty ft (PG). Link to 572 B1 - Part 1