And the best way to know that is to do the wet & dry compression tests PROPERLY.Agreed however it sounds like the owner may not have the funds to rebuild.If the compression doesn't go up it may be a valve issue.
All we're trying to do at this point is to evaluate the condition of the engine, when that has been done, then he can make an informed decision as to the way forward.
The engine has valves that open & close to allow air/fuel into the cylinders, and exhaust out, if the valves open or close at the wrong time, the compression numbers can be lower than normal - incorrect valve timing CAN cause low compression numbers, BUT, given the variation between the cylinders that you have reported, it is UNLIKELY to be the cause in this particular case.What do you mean by the o/p confirmed engine timing ?
A PROPERLY DONE wet & dry compression test is the first step into an evaluation of the engine's condition, not doing it and hoping for a different solution or a quick fix is just wasting time.
The sooner we get those numbers, the sooner we can help you find a way forward.