Depend a lot on the placement of the factory Bb pump pick up boss. My 1/2" pick up cleared a 4.3" stroke in a low deck with just a little relieving/chamfering of the block. I've seen some 4.25" where the 1/2 pickup had to be offset drilled from the existing 3/8 hole to clear. These were both 2.200 rod journal examples though.

Generally all strokers above 4.15" need to be checked, I've heard that most 4.375" strokes run into clearance issues but I haven't built one that big. Externals are really no big deal except for the added plumbing and pan expense.