HELP! I am bewildered with my jeep Problem!

I have a 1997 Jeep wrangler sport I-6 4.0L 5spd manual trans. I may as well start at the beginning. I had driven the jeep for a while with the exhaust being disconnected at the header due to finances. While doing so the jeep used to spuuter (almost like a backfire) when I was downshifting to slow down (back pressure?) It got worse and the jeep used to almost die untill I switched it out of gear and gave it some gas (also upon slowing down to a stop). I fixed the problem and then the Exhaust broke at a point slightly later in the exhaust chain, right before the Catalytic converter.

I was driving in that condition for about 2 weeks when I noticed a high pitched squeal or whining coming from the engine. (not a belt issue) I got home okay and parked overnight. When I headed out the next day the noise was still there and the car made it about 10 miles before I was slowing down at a light and depressed the clutch. I got a sound from the engine that sounded catastrophic and the jeep didnot start (sounded like it had trouble turning) I spoke to a mechanic and he said it could be a starter or an siezure of teh engine. He said to see if teh engine turned. It does and I replace the starter… Nothing! All my gears are turning, so I have hope! please help!

To see if the pistons are still connected to the connecting rods and crankshaft, take out all the spark plugs, insert straws into the spark plug holes, turn the engine over, by hand, while observing the straws. Do the straws all go down the same amount? Does the engine turn over easily, by hand?
To see if the timing chain jumped, remove the valve cover and observe the valves. Does #1 cylinder valves close at tdc compression (crankshaft on 0 degrees)?

thanks for the reply… All my belts are hooked up so it is a bit difficult to turn the engine by hand. Sounds like I need professional help…

And the mileage is??