Tonight, I finally had the time so I set out to get it all installed on the Stella.
The hardest part of the whole deal was installing the valve stem, but only because I was Working Stupid for five minutes, trying to push it through with my hands. As I was fighting with it, I was thinking, "the guys at the tire store obviously use a tool for this..."
Once I went downstairs and got a claw hammer and a rag and used the claw to pull the valve stem into the hole, the stems took about five seconds apiece to get installed.
Then, I ran small bead of grease around the groove for the o-ring, o-ring in, a little more grease on top and it was time to button things up.
All greased up:

The o-ring

The bolts for the rims are captive. This also allows you to tell which are the rim bolts and where the lugs should go.

The bolts are just long enough to hold everything with the rim flush to itself, so in order to get it together, I started with just the flat washer and nut, then went back and added the lock washer to each nut afterwards.
Tomorrow, I'll head over to the hardware store and pick up some acorn nuts to replace my lug nuts & the rim nuts. I saw the picture of that someone (WillyB?) posted the other day and that looks pretty sharp.
Then, the moment of truth. I grabbed my bike pump and inflated to 1.8 bar/25.75 lbs to get a bead...and it worked like a charm

By this point, it was dark, but I didn't care. I was going to get out and take a ride.

And does it make a difference? To some extent, it's hard to say. I only rode a few miles and I've taken so much weight off the bike in the past few weeks that it's changed its handling a fair amount just from that.
I've removed the rear rack & milk crate (~10 lbs, maybe more), the spare tire (~15 lbs), and replaced the tires (~2x7 lbs), for a total of 40 lbs of weight off the bike. I definitely felt improved acceleration just from that.
The K61's are nice & sticky. They gripped the road through everything I tried, which admittedly wasn't all that much since it was dark and I was only in my neighborhood. This weekend, I'll get out, take them on the highway and run them through some curves to see how they do then. The highway will be the real test case--will this thing now feel safe & stable up past 65mph or so?
I won't really be able to say how much good this all did until I finish setting up the shocks, but at this point, if it's not handling well, that's all on me and not the parts.