I am at 107k miles on my 97 and I know many have experienced higher mileage.
Question: Are these heads/valves/ stem seals/springs etc reliable to 200k+ miles without a rebuild..?
Or since I am about to do the UIM / LIM should I get them redone now as preventative maintenance?

My valves are not the quietest in the world right now and have been adding lubgard blue bio engine treatment to keep em shut up, which seems to work.
Just trying to get some opinions, have a local machine shop that can do the work.
They are a bit noisy when cold but seem to be fine once warmed up.
No smoke or anything..Compression test 2 years ago was fine..

not something i would worry about. taking off the head adds a bunch of uncertainty, the exhaust manifolds are a pain in the butt when you live in rust belt areas. plus you sometimes have head warping that occurs from taking the head off and on. alot of people have no issues further in than the LIM for 300k.

personally i have had better luck using a good quality dino oil like valvoline to keep things clean and quiet. when i have used synthetics or additives it has always been worse in noise and efficiency.

I would say if anything, lifters and rockers, but that'* only if you really want to be anal about it.