Last summer I bought a JDM* J18 motor from Foreign Engines, Inc. Foreign Engines IIRC it was about $1k (delivered) and was from a front wheel drive car, so only the long block was used. They had to "look" for a J18 but had J20's sitting around. (last year) They are the ones who advised me to NOT try and "upgrade" to a J20 or larger due to the crank sensor issues. They couldn't tell me why, but had customers that had had problems... none had solved it. (I learned it is the actual crank and computer mis-match due to the number of teeth on the crank itself.)
I FINALLY got the motor in, installed and I started it the other day. Other than running a straight pipe down and out the side, it sounded good. It is in the muffler shop getting a 2 inch system installed. I need to time it and some other items this weekend. Emissions and registration next week.
While I haven't ran the J18 long enough to know if I am "happy" with it, my other "Kick" has a G16 from the same place. I have been driving it with no issues for about 2 years. I am happy with it. When I took it through emissions testing, I was told it was cleaner than most new engines.
Note that due to the age of the TracKicks we need motors from, they are getting rarer from as JDM,
OBTW: You can use the J18 long block from "any" front wheel drive Suzuki car. Check your local wreaking yards and maybe Craigslist. Note that engines from you-pull-it yards should be considered no better than core motors until proven to be better.