[SEL] McComick-Deering Model M - Exhaust timing

[Paul]

Hi All

It has been a while since on this list, but finally got back to working on
an engine.  I have a model M 1.5 hp.  It ran for several years, but has not
run for a couple of years.  Upon trying to start, I had no compression, so I
pulled the head, crank bearing cap, and pulled the piston.  Rings froze, so
I replaced. After doing this it would not start, upon checking the timing
marks per manual, the exhaust is 180 degrees off.  

My question is, did I do something I am missing, or could it have run before
like this?  I really hate the thought of pulling the fly wheels and side
cover to check the timing marks.  My second question is, can I pull the gib
key driving the cam and turn it 180 degrees and replace the gib key?