I may not understand the question. But, if I were making a new A frame for the front of a vintage trailer, I would determine the room needed between the front skin and ball to house the tanks and jack. The point where it’s welded to the two main frame members is a given. The angle varies with the length of the A frame. If you want it identical, maybe someone will measure theirs and post the dimension. If I had rebuilt mine on the 55, I would’ve made it 6” longer to allow more room. I know the length has a lot to do with the weight distribution and how it tows, but a few inches doesn’t scare me. Good luck.
Sorry for the confusing question.
I’m replacing the Airstream original Marvel coupler. The A- frame angle measures 60 degrees - eye balled with protractor.
The replacement Bulldog coupler is spec’d at 50 degrees.
Did Airstream ever publish the angle used?
Not sure about vintage AS but the Typical A-Frame is almost always 50°. If your trying to measure the angle of the tongue you would need to put the center of your protractor out past the end of the tongue tubes where the outside edges of the tube would theoretically intersect. You could also clamp to straight edges to each side of the tongue to get your intersection point hope that helps
If that can help:
I just change the coupler on my 79 excella 500 with a standard 50° coupler found at harbor freight without any problem. Match perfectly, except the tongue jack is not a the exact same location.
So unless they change the frame angle between 70 and 79, 50° should do. If you want to be sure you can go to your local hardware store get a couple and see how it fits without welding it, if it does not you bring it back
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