Hi fred,
well the grinding when you put it in gear is most likely the syncronisers being worn. Putting in a heavier oil may help quiet it some but instead of using the 80w90 try the ligher 70w oil. If the oil is too thick it might make it harder to shift when cold.

As for the propane problem it sounds like the converter or maybe the fuel lockoff, my guess is it has a century converter? the lockoff may be built into it.
I checked my cat service and parts program but that truck is so old it doesnt show any service information, only parts.
sorry i cant help more, maybe someone else here may have an old hardcopy of a service manual laying around.