rear frame tube type/rebracing?

Hey guys, I have a 650 and just recently cropped the rear end a bit. I know the proper way to cut on a frame is to weld it to a table as to retain straightness, but I do not have access to a nice shop. So...out came the hacksaw - the very rear of the frame (~3" past shock mounts) is larger diameter tube which ends. A smaller diameter tube is U-shaped is stuck inside to tie the rear together and welded. This is what I chopped off. Once cut, the U-shaped piece sprung outwards about 1/4". I've heard this is because the bike has had a rough life and the frame is under tension.
The questions:

Is that 1/4" a big deal? Should I recompress the ends so they are at a similar gap when rebracing?

What kind of tube is the frame made of and what should I look for for in a bracing tube?

I am planning on just torching and bending a U out of the smaller dia. tube and fitting in the ends similar to stock, only much shorter and cleaner. In the future I may go shorter yet, but for now I will use the stock seat pan.

Thanks for reading this long post and for any advice you may have....

its going to be really tough to bend that tight of a radius without king the tubing,how about shortening the piece you cut off and reinstalling it with some slugs?id also suggest atleast raing the bike up from under frame with both wheels off ground to remove any suspension load on the frame before welding it back together.