The M has a low compression 4-banger so if it will pump up 55 psi or more then it should run. These engines could run on distillate if that was all you had. They have to have enough draw to take in a fuel air mix so it has to have some compression. As was already mentioned, blow by will tell you how much is getting past the rings. Many of these old engines have sleeves so they aren't too bad to overhaul since no boring of cylinder walls will be necessary.
If you crank it with the spark plugs out, it should blow your finger off each one of the spark plug holes. If it can't do that then it needs more work. Check for spark from any of the plugs grounded against the block. If it has fuel, spark, and compression it should start.