Yes, they are both 66 inch tractors, sorry I should have mentioned that.
Here is some information on serial numbers that maybe you can confirm.
In 1997 I attended the Massey Ferguson 150th Anniversary Celebration in Milton, Ontario. There I met Brian Mc Govern who had researched the Massey archives for the GP serial numbers versus years produced. This is what I recorded in my notes.
1930 - 300001 to 301417,
1931 - 301418 to 302851,
1932 - 302852 to 302979, these first three years production all used the Hercules OOC flat head engine.
Starting in 1935 the GP was equipped with a valve in head engine, Hercules OHC, serial numbers 303001 to 303400. Apparently these were all produced in 1935.
I don't have any contact information for Brian, I think he was from Ottawa, Ontario.