I would offer to check the valve clearances but listening to the thread and the poor bikes lack of maintenance I fear that some of the valve clearances would need adjustment which if it is the engine I think it is, is a cam out job. Then you need someone with the right shims, which can be a pain as most dealer don't carry the full range.
If you check the valve clearences it make sense to have changed the oil and oil filter after not before, so any muck that got in the engine while checking is flushed out at the oil change!