what are these guys doing to the rear frame horns to get the bonneville style rear push bar? I have this so far. I want this.
There's no horns on that coupe. Cut them off. You could mount the push bar from the center of the crossmember.
When they run the curved rear spreader bar or the push bar they are shortening and stepping the horns to get the spreader tucked up tight to the body
A push bar doesn't equal a rear bumper and if you are building a street car, you might be ahead to check with your state laws first. JMTC
Check this thread out for a good example of rear horn shortening. https://www.jalopyjournal.com/forum/threads/another-deuce-rdstr-project.1138730/
As Krylon said, the Bones step up the rear of the frame tighter to the floor. They usually curve the spreader to match the body.
Here you go. Illegal to run a car in Illinois without a bumper: https://www.ilga.gov/legislation/publicacts/fulltext.asp?Name=093-0702&GA=93
I'm really amazed that someone on here would question the legality of not running bumpers. Anyway, I think if 65standard has the horns that were lopped off, it would be easy enough to set the body back on and cut/angle/modify them in some way to match the contour of the bottom of the car so they come out where you want, then pull the body back off and weld them on. That's hot rodding, every one is going to be a little different. That's how I did my roadster in my avatar.