I am in sort of the same boat. I was planning on installing ARP studs in my 2-bolt 454. However, if that is going to require a line bore anyway, I might consider finding some stock 4-bolt caps cheap and having the additional work done.
The 400 SB I had work done did need a line hone (and not a line bore) after the main studs were installed. At least that is what my machinist told me. Did I just get lucky with that?