And the 4.375" stroke, 6.635" (BB Chevy journal) option:

CWmax = 2(Rod - Stroke/2 - Pin/2 - Pthick - Clearance)
For example:

CWmax = 2(6.635 - 4.375/2 - 0.990/2 - 0.180 - 0.60)
CWmax = 2(6.635 - 2.188 - 0.495 - 0.180 - 0.060 )
CWmax = 7.42" dia

The dia of the "cam cut" on my Callies 4.25" stroke crank was 7.32", with the rest of the counterweight larger. So you could design the piston with more meat, if desired (.220 vs .180)