Quoting gvr4ever:
I thought JDM could come with a small 16g turbo, 510cc injectors,cyclone intake, and a IC upgrade, over US spec. Not sure about a 89.
If it's a 89, it's most likely a Pre-facelift VR4, so basically just a RHD version of the US spec VR4 with the Japanese spec bumpers.
The production date typically is in the door jamb, however not sure if its the same for Japanese Spec cars. You have pretty much all there is for "JDM" parts stock on your car, so if you are looking for performance parts then you would look to jnztuning.com, Extremepsi.com, etc. For FMIC and piping upgrades, you are pretty much on your own there and will need to fabricate something up to suit or adapt a 1g dsm kit over. ETS stopped making a GVR4 specific FMIC kit several years ago. Most parts are going to be interchangeable, but also some stuff might be specific to your year like the engine wiring and ECU.