the other thing that I can think of to check is to make sure your valve lash is not to tight.
that is the valves not closing all the way.

that timeing mark looks ok.

the other thing that I have heard of is the crank pully slipping on the dampener.
that is the rubber part slips so the crank key pin is not in the correct relation ship to the timing mark.
so you can never get the timing set.

how are you doing top dead center?
are both intake and exhaust rocker arms loose? they should be on TDC.
is the piston all the way to the top also.
use a soda straw through the spark plug hole to feel for the piston.

just some more thoughts for you.

let us know what you finaly figure out!!!