Based on the type I think you have, the 20 cutters are as follows:
7 beading, 1/8,3/16,1/4,5/16,3/8,7/16 and 1/2 inch
10 plow or dado, 1/8,3/16,1/4,5/16,3/8,7/16,1/2,5/8,3/4,7/8
1match, 1/4",
1 sash, 1 1/2"
1 slitter
Cutters probably have 3/32" wide slots that engage the cutter adjustment mechanism, except for the 1/8 & 3/16" plow/dado cutters which still have the 3/32" diameter holes.
The cutter box is probably 4 3/4" wide X 10 1/8" long X 1/2" thick.
All information from Dave Heckel's book "The Stanley "Forty-Five" Combination Plane".
Mike