Over time the 3rd party tensioners have had failures, like 3rd party fuel pumps, they can be fine but..............sometimes not
The replacement motorcraft tensioners(and fuel pumps) don't seem to have that failure issue
No, there would be no old stock motorcraft tensioners around, and even the old ones were not 100% failure rate
The design flaw, as far as I know, was in the spring Ford spec'ed inside the tensioner, it would break, or lose tension
The spring is only needed on startup, then oil pressure takes over to hold tension
But when the spring failed to hold tension on start up, the long chains would slap the guides very hard, over time the guide would break away from its holder, and "the rattle" would start, on startup and then mid-RPM, damage done
Ford originally thought is was owner service neglect, not changing the oil, so oil passages for, and in, the tensioners were getting clogged up
So took a few years to get past the "blame the other guy stage" and get down to the actual problem
After 2002/3, the newly designed tensioners are in the assembly plants, and the failure rate for timing chains on the 4.0l SOHC drop to "regular" expected rates, any engine with TWO long timing chains will have a higher percentage of timing chain issues