Thanks everyone.
There are certainly plenty of options available to me.
I'm not looking to actually hot rod the motor, but for my purpose the added cubes would give me some additional low end torque. I don't plan on running a large carb, but may go with a lower rpm torque cam.
I've seen quite a few '02's or older with some fairly low miles, 30k or less. If I bought one of those, I'd probably pull the cam chest cover and check out the tensioner, but it would get used at first pretty much stock.
With the 6 speed Miata, that's fairly close ratio, I think I can have some fun shifting gears and cruising without putting down a foot. I doubt that many will have seen a V-twin reverse trike, so unless I meet up with a Morgan Three Wheeler, I'll be the only one around these parts in one. By the way, the S&S Wedge motor just doesn't sound right to me. Nothing like a 45 degree E-twin to lull you to sleep..... but not while driving.
Here's one of the M3W reviewers. Take a look, they're loads of fun. They claim the next best thing to actually flying. But not many of the owners are 2-wheel guys.
https://www.youtube.com/watch?v=ACPmFhDDxNUEnjoy.
Thanks again for the suggestions guys.