can anyone recommend a person in LA area to pay to install a tricky Koetsu cartridge

Scot won’t do outside work at this point as far as I know (he’s good). Brooks’ son is probably a good bet. Stirling Trayle is good, but up in the Bay Area.
I don’t think the Koetsus are the easiest cartridges to install. The stylus guard is kludgey and it is hard to see the cantilever. That said, I installed the last two stone bodies i acquired with good results. But, I’m in what is largely an audio wasteland when it comes to this kind of service. Mike Trei was my go to when i lived in NY-- he did set ups for a lot of manufacturers and dealers. There’s a big difference between "ok" and really dialed in. You can also learn while watching over the shoulder of a first class set up person and at some point, you probably should learn, but the cost of failure can be high.
Does the arm have enough mass?

Like Mike Lavigne said, the only thing that would make a Koetsu "tricky" is that it's hard to see the cantilever and stylus after you've gotten the top surface of the headshell to be plane parallel to the LP surface, which is a good enough starting point for VTA. (In fact, it's a good enough endpoint for VTA, where Koetsu are concerned.). So, have a strong flashlight handy.

Yes. Rick at Brooks Berdan. They are still open for service appointments. Plus it’ll help support local business and it will be done right.

Whoever does the setup needs to see the diagram of the interior of the Omega arm, which is pictured on the card supplied for locating the hole for mounting. The bearing is offset from the center of the mounting hole, and affects the arm's effective length/pivot-to-stylus distance. Unless the Mint protractor is made with that information, it will not be capable of providing accurate alignment.