Rebuilding a carb doesn't hurt. I keep all the old and new parts in a shoe box and can replace all the parts that could benefit quicker than I can upbolt and rebolt the carb. The old Norton Amal carbs has tiny passages that benefit from harsh chemical carb soaking, but the old JD just gets a swab, and a blast of air - if that.
Last time I did it - last summer - the carb made no difference but the points and fuel tap sure did. Doing everything in the carb, tap, and distributor doesn't take an afternoon or cost much.
I've started getting my old JD parts from Steinertractor.com, and when I stopped by my JD dealer of 40 years he said they were doing the same. Even showed me he was selling the same carb parts I had just bought. Not at all sure how that is going to end up....
For quick fuel line fixes - getting that crazy automatic fuel tap to work right - I've found that model airplane fuel line will stand up nicely to the new gasoline mixes and it helps that you can actually see the fuel.
When everything is working right, my final step is to make up a soft copper fuel line with compression fittings from tap to carb. I know it is not going to leak or burn.
What dandy machines those old JDs are! Made to be easy to keep running forever.