The first generation Ford 4.6L had chains that literally would last forever.. Typically at around 250K they would make some slight noise on a cold start, but quiet right up.. From when that began you'd have at least another 100K till you really had to worry.. I replaced the chains on a Grand Marquis I had way back when at around 320K.. Cam timing was off just shy of a half degree..
Never fear though, they fixed that in later years...