Anyone have a good source for shims that could be used to build up shaved T-Jet posts back to proper level?

Check a hobby shop or art supply store for plactic tubing. Another thread suggested using the ink barrel from a bic pen for replacing posts.

If you have any bent or broken guide pins you can cut off the excess and use the front.
For shimming I think of less thickness. You might try some sheet plastic. Measure and glue the appropriate amount of sheet pieces together. Drill the hole while you have plenty to work with and then trim. The advantage would be flat surfaces top and bottom.

I have 3 Aurora xk 140's that were sold as t jets. The factory added a black plastic spacer on the front post to clear the t jet gears. All three tilt one way or the other, two notably. (Got 2 new, they were always that way) I guess it would be better to tack any spacers on while the body is straight on the chassis if you can, then fill and finish after.