I'm not sure on the LM7 but I have a 98 GMC with L31 (5.7 Vortec) that was having some issues. 3 different independent sources said, "have you replaced the timing chain just to make sure it's not causing that?"... So I did some reading, GM says (at least for the L31) that the timing chain is made to outlast the life of the engine. I decided to do the swap anyways. I bought an OE timing chain and sprocket kit and a new dorman cover. The old timing chain, with 330k miles on the engine, was actually slightly tighter than the new OE replacement... and the new timing chain didn't solve the problem, it was a waste of time and money...
Honestly that sounds right for doorman. They're an economy brand
I'm a little skeptical of the lifetime of the engine bit. The amount of fine print I've seen with that word gives me pause.
Kind of like the whole lifetime transmission fluid thing... It doesn't mean it's good forever. It means that by definition, when the transmission fails from shit fluid, then that's the lifetime, ignoring the bit where some TLC would get double or triple the lifespan out of it.
Or the one where "lifetime" is the designed lifetime of the part. Ex 100k or 150k
This being said, if timing chains are considered a fluke failure on these motors, I won't mess with unless I have the timing cover or oil pan off. If one comes off, so does the other. Gaskets interfere with each other and I reason if one's bad, the other's not far behind. And messing with one might cause a leak at the seam where they meet. That'll be when I do the "while I'm in there" stuff - oil pickup oring, timing chain(maybe? depends on how it looks when I inspect it), water pump, harmonic balancer, and maybe a volume oil pump like a melling 295hv. That bit's very much undecided as of yet though