1958 HD-5G into the fold:

Talked to starter rebuilder this afternoon and not going any further with the 30MT. He also recommends a 39MT to replace this one. Didn't have one but will build one up from parts for me. Less $$$ to go with the 39MT too as two of the field coils of the original starter were out of spec, and one pole shoe was cracked/busted from the starter motor being waylaid with a hammer several times. There are actually dents beat into the housing. Also discovered the cylinder block in the tractor is aluminum. Head, and flywheel housing are iron, but most everything else is aluminum.

Surprised me. I've seen many 3-53 Detroit engines in both iron and aluminum when in the military but this is the first civilian aluminum block I've seen. However, I don't know much history on the tractor. It was very near dark when I was pulling the starter and a magnetic work lamp wouldn't stick to the block is how I found it before looking closer and snapping photos.