Chris,
Here is what I used to update my T-1 linkage.
For the Radius Bar, I used a rod from Lionel parts 690700E216 and 690700E217 (shown below). However, 217 is not available, but you should be able to use 216 and flip it around as it is not tapered. Note that these have a jog in them, so I had to straighten them out using a clamp/pliers. Based on where it is, it did not look bad once done. To attach to the Expansion Link, I clipped open the larger circle end and expanded it to fit around the existing pin. Then I squeezed the ends back together.
For the Crosshead Arm, Union Link, and Combination Lever, I used MTH parts EC-1110007 and EC-1120007. I'm sure you could also use Lionel's versions 6208029238 and 6208029239. The pics below show where to cut (straight lines) and what to not use (X's). On the upper cut, I just ground down the rivets to remove the Radius Bar and the Valve Stem.
Here is the close-up of the completed running gear:
