I would do a standard tune-up. You are at or beyond the recommended life of your spark plugs. If you haven't changed points and condensor since the plugs were changed you are past the recommended life of those as well. Even if the points look good you need to check the points gap (dwell) anyway. Finally, check the timing as suggested by JW51,
Let us know how it runs after the tune-up and we will come with more suggestions if it doesn't help.
Kent
