how can it affect how much lift that can be ground into the cam
It doesn't - it raises the limit of how long the tappet can accelerate by increasing the maximum velocity: V in inches per degree of rotation = (D - .040") ÷ 114.6. The .040" is a safety margin for eccentric tappet bore etc. A blueprinted engine may be safe with .020".
SBC.842" tappet: .00700"/degree
Stovebolt/GMC .990": .00829"
VW 31mm: .01030"
VW 35mm: .01167"
