take it out, replacing that seal takes more force than the fsm displays.

make good, permanent marks (nail polish rules) on your cam sprocket at one tooth and the corresponding link. Do the same on the crankshaft sprocket and the chain. You should now have 2 links marked on your chain that match the cam to the crank.
The chain will not fall off or skip on the IP gear, don't seat it. As long as you dont allow the chain to go through the block too much - keep your marks where they want to be, but if it happens, the longer distance b/w the marks goes on the banana rail side.

if you don't undo the front of the crank, get someone to help remove the crank so you can get the chain overt all those disks etc.

everything will go back to the timing you originally had

2.

you could remove the mains and lift the crank with the rods still on and hold the crank in some kind of homemade cradle.. sounds iffy and not worth your time. remove the crank.

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