Florida has a loophole for bikes over a certain age, as long as they have never been titled.
You need is a bill of sale and they run the Vin check at the DMV. easy with the 50s and 70s as many were never titled. Have to do it in person and be a Florida resident. You can walk out with a title in hand. Never been titled is the key there, also Florida residence. Have any Florida friends? a vin check for Florida can be done by any Law enforcement agency;
https://www.flhsmv.gov/pdf/forms/82042.pdf
Alabama has a similar loophole. No title needed for vehicles over a certain age (30years?), just a bill of sale with 2 witnesses. I've never been an Alabama resident, but have a piece of property there. Your intent has to be to use/keep it in Alabama. They issue reggo only, no title for old vehicles.
I've used both of those successfully, but sometimes had to make multiple DMV trips.
The Vermont route can be a little more expensive (they calculate tax based on their determination of value) but Vermont makes it super easy. Call them, follow their instructions and wait patiently for a few weeks.
I just talked to them this week to get info how to register a used bike I bought, registered and rode in Australia, then shipped it home.