gilmo, how much experience do you have using any kind of brazing torch? I ask because I've taught hundreds of people how to braze. Most beginners have certain patterns they have to overcome in order to be successful. One of those traits is not having a sense how to move the flame evenly over a specific area. I'll use an example to explain the problem. If one is painting a wall with several coats of paint, they need to do so without missing some areas and putting 5 coats on another. And they shouldn't be putting paint on the floor and ceiling. Add to that a common tendency to not keep the flame at the same distance to the work. Sometimes a student's flame almost touches the metal and sometimes it is too far away. In addition their movements tend to get locked into a specific pattern (where they retrace a pattern) when they move back and forth instead of getting even coverage.
Now add to this problem, it is challenging to access all parts of the frame with your flame without difficulty. Something gets in the way. This means you have to think how you hold the frame in like something like a Park stand so you can move around it easily at a comfortable height (I suggest having the chain stays pointing straight up). The concept of heating the area is not complicated. What I'm telling you is that from my experience it will probably be more challenging than you might think.
My advice of course would be not to do it on a 753 frame but I'd be willing to bet you won't take my advice and do it anyway. In that case I recommend practicing with some throw away frame before you damage a good one. You will learn a lot during your practice run and see what you might need to change when you do it for real. Of course cheap frames have heavy tubing that take a lot more heat before they get up to temperature. Thin wall tubing will heat up amazingly fast and require better torch control. it is really easy to go from a proper cherry red color to orange or nearly white and do some real damage.
I've seen some ugly dents trying to create more clearance. Andy Stewart made a very nice tool to indent a chain stay for more clearance. You may have already figured out a good way to dent stays but you might want to ask Andy to send you a picture of his cool tool in case his is better.
Last edited by Doug Fattic; 04-17-21 at 09:49 PM.