Hmmm, I thought the 99 spec undertray was exactly the same as US spec except the air baffle below the radiator is removed. The only thing you really need to purchase is the brake ducts. There's a thread about this with side-by-side comparison pics.

 

It is very similar if not exactly the same. I needed a new one anyway and the '99 spec one was cheaper, so guess which one I got lol.

 

I think it is with the exception of the air baffle and 2 notches on the end of the leading edge. I'll look for the link.

 

Found it... https://www.rx7club.com/3rd-generation-specific-1993-2002-16/people-99-spec-bumpers-brake-ducts-no-471687/

Strange, after looking at mine more closely, it doesn't look like the pre-99 spec one. I bought a new one back in '03 and it looks like the 99 spec except it has an air baffle riveted at the 4 circular indentations.

 

this 99spec thing reminds me of how all the honda guys are trying to look like stock hondas in japna