Was there 2 different front cab mounts on the frame used? The 54 we are redoing has a 1/2 hole while the parts truck unsure if it is a 53 or 55 has a large oval hole.

 

I've got a '53 and it has a large oval hole. Maybe it started out as a 1/2" round, but it's not round anymore....

 

I assume that you are talking about the cab mount "wings" on the frame...if so, then yes I have seen both a round and an ovel hole in them. I can't say whether one or the other is from any certain year but I have seen both. Once you assemble the front cab mounts and install them then there is no difference between the two hole shapes.