As is usual with non-standard builds using non-standard parts, it's a matter of working through 1 small problem after another. The KMiata swap is likely no problem if you use all stock Honda parts, but throwing oddball stuff into the mix tends to have knock on effects.
Case in point: Water pump and alternator belt tensioning. They do not use a tensioner pulley, but they add an idler pulley, and you shim the alternator with a washer or 2 on the bolts to tension the belt. Using a stock crank pulley, they send a belt that's the correct length for that to work fine.
An ATI SuperDamper, however, is a smaller diameter than stock, so that belt won't work.
I reached out to KMiata and it turns out they run that pulley on one of their race cars, and have a smaller belt recommendation (a 6PK1035. Apparently they don't make 7 rib belts short enough so you've got to run a 6-rib).
After getting that belt in, it was a lot better but the provided washers weren't enough to tension the belt.
So I went and got a few more M8 washers. I ended putting 3 washers under each bolt, then attaching the idler pulley. Even with that it was still a little looser than I like, so I cut a notch into another washer so it's a C-shape, and used a pry-bar to space the alternator out enough that I could put that 4th washer over the top bolt. MUCH better.
On to the fueling mods next.