The mark on the cam and the mark on the rocker arm shaft bracket should align straight up, the dowel from the cam into the cam gear should also be straight up & aligned with the two marks and the mark at the crank should be at TDC. All these conditions together will put #4 @ TDC, which is what you want when doing cam work on a gas Isuzu 4cylinder. Both #4 rocker arms should wriggle, at least one #1 rocker arm won't.
The marks on the cam gear and the chain link are used to get the proper number of chain teeth between the gears for the tensioner to work right. They will never align with the cam marks. There is a similar indicator link that aligns with a slot in the bottom of the crank with #4 @ TDC. With the #4 piston up, the cam & gear installed with the marks up and both indicator links aligned with the crank and cam gear setting marks the timing chain is installed correctly. Your cam gear mark aligns, so only the crank gear could be off, pull the front timing cover to confirm if you're convinced the chain has jumped. Since you can loosen the tensioner, remove the cam gear and chain and drop them down through the head into the timing cover and the chain will remain in place on the crank there can't be a lot of clearance for the chain to pop off the crank gear then back on, but I guess anything is possible.
'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, body ROUGH, bought new 12/4/78. A pre-P'up?
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch.