I was under the impression, but ready to be corrected, that one can just swap the skins over (unless it's MY99 in which case they're very different). Can swap the foams too if they're in better nick.

Yes, the seat skins can be transferred over no problem, so long as the donor seat and the old seat are both power/manual due to the seat back being different. Manual seats have a knob for the recliner.
As for the bottom, it's the same regardless of being manual or power.

You can swap in 1996-1998 skins to the 1999-2000 electronically fired seatair bags just fine

You can attach with zip ties rather than hog rings

Probably something simple, but a pain to pinpoint. That's usually the case with boost issues!

Well I unplugged my TCV electrically, which should directly link the red and yellow vacuum hoses. Now I get progressive boost to about 3psi with no spikes at all. So either my new TVS is defective or my original one was defective and I didn't notice it because my wastegate actuator is not adjusted ...

That looks better! You should have no problem running it like that. A little overshoot like you’re seeing now is perfectly safe.
I’ll have to check one of my spare turbos, that might actually be a normal amount of play (I know, I was surprised when I first discovered that too).

Looking good!

99commutervolvos70 wrote: ↑05 Mar 2020, 21:49 20200305_070725.jpgMade it to 280,000 miles

I hit 280k last week. But I didn't take a photo so I guess I can't claim to be first.