Smog issues.

I own a 89 GMC S-15 wich is basicaly the same thing as a 89 S-10 with the 4.3L V6 as far as I can tell. I want to go to multipoint injection on it and I was wondering if its legal to swoop a mpfi system and computer off a newer 4.3L and toss it on my engine... Basicaly, are there any mechanical differences between the old 4.3L and the newer vortec 4.3L that a smog refferie would be able to notice?
Also, I know most of you guy just throw in a V8 and call it a day, has anyone here converted there DPFI V6 to a MPFI V6?

Thanks.