Unless there's something else, a fairly common bushing material is 660 bronze.
The stem area vs. tappet forces shouldn't be any worse than they are in the VW - it should work.
You'll have to plug the hole in the annular waist area to make a drain from the pushrod cup feed the contact surface hole.
The TF tappets can be rebuilt by the manufacturer - new axles, needles and rollers, polish the body, etc. so they need not be perfect. In a GMC (or early stovebolt with no hydraulic tappets) the tappet's oil feed area is harmless, but in a late 235 you have to measure where this is vs. the tappet oil gallery to make sure it's open front to back, and no leaks.
