This statement makes no sense to me, "TDC" is the same as having piston #1 at the very top of it's stroke, Top Dead-Centre, what you have described here is (assuming the part about the piston being at the top @ 2 o'clock position is correct) seems to describe you setting all 4 pistons level to one another. This would be 90* before/after TDC.The crank is at tdc when the blob is at the 10 o'clock position, piston nearest the timing chain is at the top when the blob is at 2 o'clock
I'm not the best at describing these things, but in the simplest terms I can think of, are you setting the timing with piston #1 at the top, or halfway down? it needs to be at the top
I would try to set it with the rockers removed but pushrods in place to avoid any damage/lockup while setting up, then set the crank position so you have piston #1 at TDC and mark the sprocket relative to the crankcase to help know where TDC is in future.
Then once you have a definite TDC setting at the crank sprocket, turn the camshaft until you see the *inlet* pushrod for cylinder #1 just begin to rise by maybe 1 or 2mm (the *exhaust* pushrod for that cylinder may, or may not, also still be moving down depending on valve "overlap" for this engine). With the piston at TDC and the inlet cam just beginning to lift that should be close enough to the correct timing for you to slip the chain on and tension it.
Before you reinstall the rockers, rotate the crank 90* (so all pistons are level) to avoid any valve damage if the setting is wrong, bolt the rockers down and turn the engine slowly by hand a few times afterwards to make sure nothing touches.
Depending on how coarse/fine the teeth on the timing sprockets are, this should get you within a tooth of correct timing if not spot on. (note, the ignition timing will need setting again afterwards as it may be 180* out)
Finally, once you've got it all timed up and known good, make your own permanent marks on the timing gear for future reference
HTH
