JDM vs USDM b16a internals? same?

I can't find anything on the net... but i imagine a JDM b16a has the same internals as USDM?? as far as rebuilding would go, like could i use b16a2 specifications etc for jdm b16a? and what is up with motors coming from japan with only 30-45k miles? like 90-91 SiR b16a with 30K miles? wtf why do they pull their motors that soon lol

Just the piston have a slightly higher compression, so yes use the same specs.
They're are usually 30K-45K km. But that's because in Japan they have some expensive re-registeration for older cars, or emissions checks or something along those lines. So instead of going through the hassle, they just sell the cars or send them to the junkyard and buy new ones.