hey rob
the only difference in the chain kits are the ex sprockets the rest is the same (fitted a yh kit to my z22se just dumped the ex sprocket 🙂 )
fitting a new tensioner to an old chain won't remove the fact the chain is stretched the new tensioner will move out to the same place as the old one and a pointless exercise unless the chain has less than 20k on it
valve damage will occur if the chain breaks or jumps to many teeth if they have not made contact with the pistons thats a good sign its not jumped
with bent valves you would see the cam followers loose or out of place even before removing the head
my car had an over stretched balancer chain at 55k the main chains seem to be around the 70k mark to show signs of immediate replacement with the chains i have done i would recommend changing both chains if your car has 70k or more on it if not sooner depending on the sound of the engine
the z22yh's and the later z22se like mine seem to get thru the balancer chain quicker than the main chain
all z22yh's will be fitted with the lager style oil jet and the rev 2 tensioner it is still a good tensioner the rev 3 (z20net) just has a circlip in the end to stop the piston dropping out when the chain get to slack
hope this helps 🙂