It sounds like your front brakes have changed out to the 911 setup but what year I don't know. I don't think the C2 caliper will be a bolt on item. The rear C2 caliper I know will take a lot to make it work and you lose your rear parking brake. The late 89 to 94 911's model # is called "964" (95 to 98 is 993, 99 to when ever next change comes [07?] is 996)
Anyway I found this website that may help you out. You supply the calipers they make you a bolt-on kit.
www.vehiclecraft.com/Brakes/vciweb0.htm
Then scroll down to where it says "911, 914/6 using 964/944T/968 type caliper upgrade". They should be the kit you need. Hopr that helps
Ralph