[Randy in ca]

The two rear blocks are taller than the others because they fit up inside the subframe rather than under the cross sills. I have some dimensional pictures of the ones used for 1928-29 I can send if you want - I'm pretty sure the 30-31 ones are the same except for their length - believe they were made longer in order to reduce cracking of the subframe. If nothing else this will bump your post up again and maybe someone else can add some info.