One note, make sure the "T" mark
corresponds with the piston
being at top dead center.
Just insert something in
the plug hole to verify the piston
and "T" are in sync.
If the "T" marks are accurate then
the cam gear can be aligned safely.
You should be okay as long as the
rear piston is at the top "T"
and the valves are closed and
the cam gear mark is aligned with
the mark on the top center of the head.
This puts everything in the right place
at the right time.
As long as the valves are closed when
the piston is at the top then
no damage will occur.
If your timing was correct originally
then the marks may align if you
turn the engine over a number of times.
It likely hasn't changed if the chain was
This might help: