good as well for replacing are Newqida trucks. (sometime one can get whole newqida cars cheaper, than a pair of trucks from LGB or Piko)
gauging, regauging, replacing, or even manufacturing wheels or trucks in "G-gauge" is no rocket science. one can get away with nearly everything.
the only "secret": make the cars heavy enough! (most important for pony-trucks on locos)
some proof of my crimes:
the shown above wheel-sets on a scratchbuilt:
from a bump-n-run toy to a run-and-dump toy:
turned by the village smith in plastic (left) and iron:
bump-n-run fake-loco:
they all had one thing in common - they kept me rolling through the low-budget years.