Just an update on a similar note - I have likely the world's most mentally unstable line bore setup. As someone guessed above, yeah it's a little bit too quick, but it's doing the job thus far. I figure if my plan here doesn't work, that I'll just do it again and learn more. For some dumb reason I'm just doing this with items I have on hand. Centered the bar in the bore with a 3d printed insert, then checked parallel with the upper bushing a few inches out.
The feeds and cuts need to be very light, or it's worlds of chatter. As expected, on the "pull" cuts, the taper on the chuck would pull out. It's okay, welded it in place. Then I got tired of the boring bar slipping in the chuck, so that got welded too. I'm doing partial bores from both sides to whatever gives a stable circle. After that, I'll machine sleeves to lightly press in to get a shade under a 50mm bore. After that, I'll heat the end of the stick up and give the bushings a liquid nitro bath and hopefully get those set without wrecking the sleeve. I'll leave 4mm of free bore in the sleeve outside of the bushing for a shaft seal. Might tack weld the sleeve to the outside just to help it stay put.. but probably won't.
Either way, it'll be good enough for use around the property for a while. The rest of the machine is near good to go. New pins and bushings just about everywhere else, new tracks, all things checked and getting the primer all sanded for the body panels. New paint new decals and she should be right squared away. Ive had a lot of fun with this thing. Heavy equipment seems like a whole different kind of working on stuff. Big Lego pieces that you can wail on with sledges.