one sysmptom of a stretched t-chain is that the power band moves up, so if you used to have plenty of power at 2000rpm, and notice that you have power at 2500 or 3000 instead, it's a good bet that the chain is stretched.
on a distributor motor, having to bump timing was a good sign, with computer control, the computer does it automatically.
on the old ford 302's the nylon gears were for noise control, and with the normal heat/cool cycles of the engine, and the hot oil constantly washing over them, the nylon would chip off. most replacement gears were solid unless you got them from ford. old chains were good for roughly 70k-80k
a test, is also to pull a valve cover (unless you can see a rocker without pulling it) and slowly rotate the engine forward untill you see the rockr move, then stop and slowly rotate the engine backwards untill you see the rocker move again, the amount of rotation will give you the slop in the chain, tensioners reduce the apparent play slightly, but not a great deal.
The BEST way with the older 50 motors was to pull the fuel pump blockoff, and feel the chain.
an odd developement I've noticed is that older cars, if you had the chain out for some reason, you could tell if it was bad if you could lay it on the table so it was a loop sticking up, and touch the center together, modern chains come curled up in a small box, so it's no longer a good check.
ken.