[S-mk3-B]

You can use a JDM engine, you just have to transfer over the EGR components from the USDM engine to the JDM and whatever else (pretty much put them next to each other and whatever the other one doesn't have just simply swap over), hence using the same ECU will be fine. While it's out you should do as much as you can cause even if you get a "low mileage" JDM engine, they could of been sitting out anywhere and who knows what the internal condition may be. Anyways at least change all the seals like front and rear seals, valve gasket, water pump, etc.. And if you want to go the extra mile you could do a head gasket job w/ ARP head studs (cause the 7mge/gte engines are prone to BHGs). Other than that have fun and welcome to the Supra life!