Synchros you can get from kormex...talk to Young, he did it awhile back.
As far as the mods...I'm with Twisted...you should decide whether you want to mod it for personal use, or fix it for sale purposes...because it seems to me like you havn't quite decided. If it were me, I'd replace the driveshaft and clutch with OEM.
Alan mentioned some good ideas regarding clutches, also if you check out 3si, there are dozens of great threads regarding clutch decisions.
Lastly, the active aero...have you taken it apart, cleaned it and put it back together...many times this is a free fix that repairs simple lock-ups. I'm pretty sure I have something in the FAQ about this, but if not, there are instructions on
www.vr4stealth.com