Typically I'll pull it to within a degree or 2, check it and then just touch it up to get it exactly where I want it. Might take a couple of test fits but that's better than trying to pull a few degrees out of 1.625 4130.

That sounds like the safest bet. I don't see myself taking some bend out of C/M. That stuff is pretty stout.
What do you guys use for hole saw blades when making notches? I tried cutting some C/M with my sawzall using DeWalt blades. Killed 3 new blades within seconds and barely touched the tubing. Ended up using a cutting wheel on my 4" grinder to cut the tubing. Normally cut to length with my chop saw, fishmouthed on my bench grinder.