Vacuum boost brake conversion

[72kat]

I have a 72 c10 with a 350. It has disk brakes on front and drums on rear.
I want to convert to vacuum boosted brakes for better stopping.

I have been looking on Summit Racing and Jegs for the combo. master cylinder, vacuum, proportioning valve, etc. I see that there are different diameter vacuum boosters. 11 inch and 9 inch.

Thought I read that some guys ran into a conflict where the booster was too big and causing problems. So with a 350, what size should I get?

Thanks.