So looking down the exhaust it's actually stopped at top dead center not BDC. The gears aren't jammed either. I haven't taken the head off, but if this as unusual as it sound I might just send it back to the distributor.
To rephrase the problem the piston will only move down backwards. Any more ideas?
Maybe time to pull the head, it's quick and easy.
Your needle bearing may have exploded and one of the needles
is jamming the piston to the bore.
or
a piece of ring broke off and is jammed in the transfer port.
or
Your crank bearings are partially seized.
or
A ring pin came out
or
the wrist pin circlip came out
I once had a aluminum head gasket that got squashed out so that
a small piece broke off and went down the side of the piston.
Pull it apart and see. Sounds like a gonner anyway.
Now you got my curiosity up......