Difference in Block Castings 31 -33

OK, I am figured out a little more about these two engines:
1931 8-98 block casting number of GU100 D (C1) GU74969 (Late 1931)
!931 Spare? with a block casting number of GU100 CC (H25) GU68870 (Early 1931)

With this block casting is there a way to figure out what model a G1000 is? All of the parts look to be comparable to the other two GU's , is there a way to find out if they parts are interchangeable?

1933 8-105 with a block casting number of G1000 (M28)

Serial number data

We have a 1931 and 1933 along with a spare engine I think is a 1931. I am trying to find out what the difference is if any in the casting numbers. Are there any major differences between these other than the 31's are 98 and I believe the 33 is 105?

Today while working on the 1931 spare engine we notice the passenger side motor and generator mount is removable with 3 bolts but on the 31 and 33 engines we have that mount is cast into the block and not removable. I looked in the parts list the part A2-164 Engine Front Support appears to be removable I guess up to engine number 73271.

1931 8-98 block casting number of GU100 D (C1) GU74969

1933 8-105 with a block casting number of G1000 (M28)

!931 Spare? with a block casting number of GU100 CC (H25) GU68870