Hey Jim, I could use a 26mm plugged pump for an engine I have in the works... would a 30mm be better for .060" line bored case, or does it matter?
.060" is a big cut.
What are you using the motor for? Tight rod side clearances? What kind of climate do you want to drive it in?
Loosey goosey clearances, line bored case, hot weather, used as a driver, I'd go 30mm, but make sure you use stock relief spring at pressure valve, and I'd use an adjuster-bypass @ cooler valve.
If you're building a dragster to just bracket race with, the 26mm would work,... or a motor with tight clearances, cold climate, tight case.
My '67 has a 30mm due to typically hot weather, and it's driven a lot in those temps. On the other hand my old Bus ran a 1679 and I just ran a 26mm with new case, standard crank, etc.