PCV issue

I would try a new valve and re check all the adjustments. The pcv is a big vacuum leak and the carb has to be adjusted accordingly. Disconnect and plug the vacuum advance when you're checking things too. A advance diaphragm leak on an older distributor can caused some rough running. Vacuum choke pull off's can cause problems too. My 273 hasn't ran right since I overhauled it 2 years ago. I've tried 3 different distributors, 2 different carbs and a bunch of different checks and adjustments. I finally figured out what it was. I put in too cold of spark plug. It's worth a check. tmm