you could probably go down to 1/32" so 0.75mm or rather than make loose ones they could be soft soldered onto the cross head and then machined down to maybe half that.
It would be possible to use bronze shim stock, if you can find someone who will supply small amounts. I used it to "bush" the yoke on a Scotch Yoke drive for the displacer of one of my hot air engines, the yoke was aluminium, and the crank pin mild steel.
yea iv thought about that just I'd have to find away of mounting that on crosshead I think the recess way is the way Togo, don't fancy soldering a thin plate, would be afraid it would fall out! And this3" scale Burrell would likely do that I guess!
Mark, a pair of little slippers could be made, a little turn up at each end, maybe reinforced with a short piece of wire soldered to the turn up. Shim bronze is available down to .005", it's usually springy.