I have a 1983 Marshall JCM 800, w/6550 tubes. It sounds great, but I was hoping someone had some recommendations for overdrive pedals.

I want something that will add some sustain, volume, and gain to my sound, for solos.

The XOTiC BB Preamp is the best overdrive I've ever had the chance to use and it will push your amp into some heavenly gain. Or unholy territory if that's your thing. A good BK Butler Tube Driver is what I'm using right now but I have a Zakk Wylde Overdrive that isn't half bad, it's just a little unreliable.