I was wondering if anyone could tell me, or let me know if it was possible to convert a 3000GT SL, to a VR-4 version?  

No, or at least, it'd be extremely difficult and not worth the effort. You'd have to take the entire engine, suspension, braking system, fuel system, active aero parts, and AWD drivetrain from a VR-4 and put it into the SL, in which case it would be easier and cheaper to get a VR-4 in the first place. You could probably drop the turbo engine from a VR-4 into an SL, but I don't know if the SL's FWD drivetrain can handle the extra horsepower. At the very least, you'd get a ton of torque steer. If you want a VR-4, save for one and avoid the trouble of a conversion. And make sure you do your homework on them. Get one that's in good condition from the start and do regular maintainence, because AWD Mitsu's are complex and will quickly deteriorate mechanically if they're not maintained properly.