Life intervened....
Parts are in. Got the wheel and hubs measured today. Confirms everything which is fine.
Hub matched exactly. I was wondering if there was a trick or add-on piece for the caliper measurer. It's got the points on it to be very precise but those aren't long enough when it's on a hub. I can eyeball it, that it matches my numbers from a similar hub, but it's not the same as having it touching. The calipers need longer finger/pointers somehow.
I measured both hubs just in case... No issues.
ERD on the rim was slightly different. I got 577 or 581mm depending on how I measured. I double checked the longer tape vs. a shorter stick. They both matched when I lined up rulers. One is a tailor's flexible rollup tape, so I thought it might be streteched out. It wasn't. The other was the Park spoke ruler. I had two nipples in opposite holes, used old spokes, had them pulled as tight as i could with tape.
Nipples are 12mm, so 24mm added on gives me... 605 or 603mm.
The pro wheel builder spoke length calculator for this model rim is 601mm ERD though. I'm thinking that's probably more accurate or it's close enough.
Original calc, with site's ERD for my exact rim.
Left spoke length: 290.8
Right spoke length: 289.4
My longest ERD measurement of 605mm.
Left spoke length: 292.8
Right spoke length: 291.4
And I've already got spokes that are 290 and 292mm. Dang.. I was going to measure those today too to see if they're a little long or short. Easy enough to check later...
So...
The site's calc meant I would use spokes that were slightly longer (slightly being .6 and 1.2mm extra).
My longest calc is means my 292/290 spokes are .8 and 1.4mm too short.
I tend to trust the site/manufacturer more than my own measurements I guess. I was getting a 3mm difference when I measured. And add fatigue -- I measured ERD after checking the hubs.
I debating on whether to lace up the wheel "dry" with no spoke prep, so I can focus on lacing it up without worrying about the prep drying up on me. That was a thought, but I think it also means I'll have to undo 36 nipples to apply spoke prep. That still gives me time with lacing though, which is the unknown part.
After that I'll see how the 290 and 292mm spokes work for sure.
When I put the 36 spoke, 135mm hub, on the bike, I'm thinking the derailleur won't quite line up but I can mess with that later. The current/old/32 spoke rim is shot, so these replacements are the future. As long as I can pedal with some gears, that would let me keep riding it.
Once I've got one wheel done or as done as I can make it, I can order more spokes and the second cassette and prep up the second wheel, adjusting anything I learn from the first one.
For the Mavic rims being "black" they have a giant shiny, silver brake strip around the outside. They don't look as black as I was expecting, which is fine. I would have gotten silver if I could find it. But the black is so slight I don't think I'll notice it much at all. The black vs. silver hubs, even less so. That's how I'll distinguish the wheels though -- black vs. silver hub.
I've hit some bumps, normal enough ones, and noticed my wheel brushing the brake or something. The wheel continues to die. But I figured if I needed to, I bet I could prep a wheel over a weekend.