timing chain?
 

Does timing chain require replacement after a certain amount of miles?

Yes. Fortunately LX & GT 5.0 uses metal gears for cam and crank (older 302s used aluminum cam gear with nylon covering, it made it quiet but would self destruck at 100K) but the chain still streches. If youre planning on changing cam You definately need to change it, but if not you can sometimes get by wth 200K on them. A simple check to do is pull the distrib. cap and watch the rotor as you turn the crank (15/16 bolt in the middle on pullies) and turn clockwise and then turn counterclock wise and watch how long it takes for the rotor to start tomove again. There will be a small delay but if if you back it up more than 1/8 turn then your chain has a lot of slop in it.

When i swapped my ported heads and put in the cam, i was on a budget, and just got the chain from the dealer, still use the factory sprockets, everything's been fine so far.

any other opinions on timing chain replacment? how long they last, etc.

Timing chain and gears are cheap insurance. If they have over 15,000 on them I wouldn't even consider re-using a set. They should last close to 100,000+ miles though.

Cheap insurance!!! The three piece set (cloyles) is like $20 at Autozone.