That's what I run on my 75 F250 and I run a 9LB cap in Vixen. I lose no coolant out of either. There's just no need whatsoever to run a 15 or 16 LB cap, regardless of what a fifty plus year old service manual says. This is the 21st century and better ways have been figured out. No way am I going to put hard to find parts in my cooling system under any more stress than they already are. It makes zero sense.
