My 37 had steel channel running for and aft with a welded plate to bolt to the spring u bolts and a piece of flat bar running across between the inner bumper bolts welded to the channel with a tab.
This was to get the height correct for it to pass through under the bumper to the rear of the car, a tow ball was bolted directly to the protruding channel.
It was obviously not professionally made as the finished result was not very elegant
I would do a far neater job if was make myself one, but when I do get the car running again I do not plan to do any towing.
I hope that helps.
Geoff