Quick and easy:

1.047" is very close to what one minute of angle produces at 100 yards.

For .65" group at 108 yards: .65/(1.08x1.047) represents .575 moa.

Similarly a .325" group at 54 yards : .325/(.54x1.047) represents .575 moa.

This can be handled by a little solar powered pocket calculator with basic arithmetic functions.