from what i read, correct me if i am wrong
1. you first tried to crank the engine over, but it would not go past top dead center?
2. you removed the valve cover, used a rubber mallet to move the valves to see if they were stuck?
3. you found a bent pushrod?
if all this is true, this is what i suspect
when you parked the engine, you did not roll it over to compression stroke, this would have left the cylinder closed, with the valves both closed, moisture would have a harder time getting in.
i think it was parked in such a way that moisture/water got in and stuck the exhaust valve in an open position, then when you tried to turn the engine over, the piston contacted the exhaust valve, which was stuck tight enough that with more force used to crank the engine something had to give, that being the pushrod, which ended up bent.
now if it were me
1. i would remove the rocker assy
2. i would use a dead blow hammer, to work the valves up and down, and i would remove the manifolds to i could squirt some oil on the stems on the bottom of the guides and also from the top. making sure they open and close freely (the piston needs to be toward the bottom of the cylinder.
3. i would use a hammer and a suitable anvil and hammer the bent pushrod straight again... it will be fine.
4. then reassemble, and rotate the engine such that one of the valves is opened, and squirt a little oil into the cylinder past the open valve, just a few squirts.
5. put the manifolds back on, reset the valves. set the intake with the exhaust open, and visa versa.
6. put the valve cover on, check the comp release function, and set it open, rotate the engine several revolutions, and if all is good
crank it up again!
my bet is some water got into one of the manifolds, moisture/humidity, and stuck the valve.
get it freed up and it should live again.
it is possible that the exhaust valve got bent, but i think you might get lucky and that not be the case.
worst case scenario
you get to pull the head and do a valve job.
bob g