noob needs help(i have searched)

[myk]

i have searched and came short handed,
my question, although its a noob one, is that is there a difference between the usdm 240sx and the jdm s13
this guy i know, kinda smart with dsm's, told me that the s13 is like the type r civic while the 240sx is like the si civic...well that was his concept to explain it now is that true?is there a difference between the jdm s13 and the usdm?
oh and he also shared that the sr's that im looking at (potentailly) are under 30,000 miles do to the fact that they have to pay a taxt on cars that hit 30,000 miles in japan. and that it wont need a rebuild. is that true too?
sorry for the noob questions i used to be a fellow dsmer but had to get out due to non reliability
thanx
-myk_