Whether you rebuild it or not you still need to do some work to this engine to make it run right. Even worn it should run decent. So, clean it up, rebuild the carb and replace gaskets etc. All that is cheap to do. Give it a full tune up and see what you get. Once it stops skipping and farting you could decide whether it needs a full rebuild, or a valve job, or maybe reringing it.

It also depends on if this is going to be a daily driver or an occasional ride. Sometimes you see rebuilt engine for sale cheap just because some dufus pulled it to put in a V8.

54 3100 with 235
62 flatbed dump C60 with 261