I have built many 2 bolt changed to 4 bolt angle mains--It is my perferred method--however, the stock 4 bolt bbc with studs can be used for well over 1000 hp without cap walk if you stay out of detonation---
The bore issue isn't an issue at the 060-070 area---generally not even at 100 or 125 over

If it wasn't for shipping to Canada I'm sure you could get a block from down here a lot less $$$