GM Parts Direct has them for $45.00 ea, but you can use a 10 bolt plate for the drivers side. I just put my D60 in today and I used a 10 bolt plate, everything bolted up just fine. I had to put one extra washer between my swaybar disco and the plate.
Part numbers for the plates are located in the Advanced Previews Forum. I think you have to be a member to access that and the tons of other useful part numbers that are in there, like brake hoses for rear disc brakes, conversion u-bolts etc. etc.(hint hint) /forums/images/graemlins/thumb.gif /forums/images/graemlins/deal.gif