USDM GSR vs. JDM

OK I've got a two part question:
1 - What EXACTLY is the difference between a USDM B18C1 and a JDM B18C1 and what would be the differences/extra costs associtated with swapping either into my 97 LS?
2 - Why are the JDM engines always so much cheaper and have such tiny mileage? This is where my concern comes from. Is USDM better for some reason?

Thanks a lot for your help

USDM motors are 1) Easier to smog, 2) Are easier o confirm actual miles. JDM GSRs run a .6 higher compression, other than that, they are the same.

the JDM engines have lower miles and are cheaper because of heavy taxes imposed on vehicles in Japan running engines with more than 35,000km on them....so people sell their cars or swap their engines relatively young in order to avoid the taxes...

this means that they are slightly less reliable because you can not get a full history for the engine and it may have been run really rough since the owner knew they'd be ditching it after 35,000km anyway.....this means yer gonna have a smoker....maybe....

USDM are easier to get full history of engine.....mc