Rich,
I've been running the polyurethane bushings top and bottom on my MGB front end for three years now. I was warned that the suspension would be much stiffer. I think it is but it is but it's not noticable. The steering is so much more accurate now, much better for autocross courses. I also gutted the lever type shocks and installed grease nipples in the shafts to keep them lubricated. I use Corvette rear KYB shocks (with eyelets top and bottom) and fabricated mounts.
Rdorman,
The rotors I bought last time were from a 1970 Monte Carlo. I understand the the Camaro or Firebird rotors from that period will work, too. There are two tricks. The first is to find the rotors with the outer projection from the flat wheel mounting surface that is 3/4". You do not want the ones with the projection more than one inch. The second trick is to have a machine shop mill the outer bearing surface 1/4 inch deeper. That should allow the outer bearing to slide 1/4 inch farther in than it normally does. Then it will fit the MG spindles perfectly with stock Chevy bearings.
Moss motors sells lower a-arms that are slightly longer that stock to give a little negative camber. I haven't tried these but if I were autocrossing more I might. I don't think I would slot the mounting holes though. Maybe it's all the rough pavement I run over on rallies, but those bolts used to come loose often. Now they're grade 8 and loctited with lock washers and locknuts. No more problem!
I hope that helps,
Paul