Right it was a simple U bolt. In the earliest models. Lowrider racks were almost all attached with rubber lined clamps of some sort the first few years. It works fine. Forgot momentarily about the U bolts.

You can use a newer model with a clamp band and it will be fine as well. A lot were attached that way too.

I think the Nitto made bands are by far the nicest quality.
https://www.benscycle.com/nitto-clam...nd_870/product

I think Treks did get the mid-fork braze ons earliest, presumably because of their close relationship with Blackburn. It was at least a couple years IIRC before other makers started spec'ing the special braze ons. Like I set the clamps work fine; braze ons just make it neater.