69 340 problems

At 90000 miles you are way overdue for a timing chain. Pull the front cover and rotate the engine to TDC with a socket and breaker bar. Rotate the engine backwards from TDC and see how much slop appears. I'm betting around a quarter turn to take up the slop. That's how it was on all the ones I had that mysteriously quit running, and they do it with no warning. Hope I'm wrong. If this is the problem, don't forget to check for bent pushrods and valves. My best tally was 16 pushrods and 12 valves. IMO the Mopar Performance timing chain tensioner is a good investment.