Hi Ian, Mike and Richard,
It is a GM-H and you can tell by looking at the photo of the floor. The bottom corner pressings on the front and rear panel have rounded corners and FMC are square. If I don't make sense I can take some photo's tomorrow.
I think IH was the only other manufacture of type 4 trailers and there was not a 4a.
Mike is right
, I highly recomend removing 4 leaf springs from each side and the fitting of shock aborbers and then wheels stay on the ground.
Ian I pick up a type 3A hopefully next weekend I will send you some photo's when I get it home.
Jeff