Replacing the chain is done by splitting the old chain and connecting it to the new one, an assistant rotates the engine by hand "rolling" in the new chain as the old one is pulled out. Once the new chain is all the way in its two ends are connected via a master link that is crimped into place. It isn't difficult but can get ugly in a hurry if the chain is dropped during the process, it must be kept taught on both ends every second until it is crimped. If it falls it gets jammed and can break plastic guides and rails.

I can't over emphasize how important knowing that when the balancer is at zero that the piston is perfectly at top center. However much it is off in degrees will transfer to all of your other adjustments. It is the foundation for all the other steps, think of it as trying to build a house on a foundation that isn't level.

From the picture the cam gear looks good. Try to post another picture of the cam gear looking at it straight on showing as many teeth as you can.

Is there a reasonable chance that the injection pump moved since the rebuild? Although never a powerhouse, those motors run really well when all adjustments are dialed in.

CTH, I can't think of how to gain access to put something in to touch the piston on that motor to find TDC.

To the OP, TDC is best found using a dial indicator then zeroing the indicator to the balancer.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer