In the last 8 months we have had a 606 with a broken chain and a 603 with 17 degs of stretch in the chain here.
I always recomend checking the timing and degree of stretch of one of these with more than 100k on it. Still not a perfect check for chain condition but, with the costs of repairing one that popped a chain, cheap insurance.
Just be sure to look at the gears closely as well.
There was a bulliten on the earlier 603's as well.
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.