Question: How much Vacuum needed for headlights?

[Ed's 1970]

Hi guys, I am going to be putting in a 540 big block in my car. I want around 600-650 horse, so the cam will probably be in the 240-250 range at 050, solid roller. How much vacuum is needed to keep the headlights and wipers operational or should I just hook them up to an external vacuum canister and not worry about it. I have manual brakes right now, but there is a possiblility I may convert to power brakes. Any suggestions?
Thanks a lot,
Ed