Recently a friend of ours John imparted this story to us. Last weekend, I traveled 1.5 hours to personally remove a complete front disk brake assembly from a 1970 Chevrolet Impala convertible. The disk brake setup will be replacing the front drums on my 1968 Caprice. As always, I recondition any parts that I swap onto any of my cars including this brake setup. Here is the problem The donor rotors and the calipers are not standard parts for the 1970 Chevy Impala as per the books and when actually matching up the original parts to the replacements parts they are not even close to being the same. I tried several auto parts stores with the same results. The replacement rotors are noticeably larger in diameter and the distance between the bearing races when measuring back to back as they are seated in the rotor are about " deeper than the donor parts. The calipers have different hose positions among other differences. The counter person at my local NAPA tried to match up variations of Malibu and Monza rotors which were also noticeably different from the original too. We are baffled.. Chevy use non-Chevy brake assemblies during this era?

I sand blasted all my parts and have a lot of part numbers EXCEPT for the rotors. The rotors had absolutely no identification numbers that I could see (maybe the rust of many years took it's toll on any numbers that once existed).
The following is all the part numbers that I could get from the disk assemblies.
Left Side disk assembly break down:
Caliper -> Delco Moraine 5488316
Splash shield -> 3953421-L
Caliper mounting bracket -> 3974858
Tie rod arm -> 3966187 GM132DY
Spindle -> GM 85 (the 85 is not too clear in the casting)
Outer -> Tyson M12649
Inner -> Tyson LM48548
Grease seal -> C/R 19768
Right Side disk assembly break down:
Caliper -> ? (NAPA had this caliper for matching purposes)
Splash shield -> 3953422-R
Caliper mounting bracket -> 3974858 (same as left side)
Tie rod arm -> 3966188 GM14PA O
Spindle -> GM 80A
Outer -> Tyson M12649
Inner -> Tyson LM48548
Grease seal -> C/R 19768
Original rotor specs as I measured it:
11" as measured across the rotor. When measuring between the bearing races back to back as it is seated in the rotor the distance is approximately 1 5/8".
I followed your suggestion and bought rear rotors for a 1968 Corvette (which is the same part number for Corvettes from 1966 to 1980) to retrofit to my obsolete 1970 disc brake assemblies. After spending many hours at Napa earlier this week attempting to match up all sorts of rotors with the original Impala rotors with no luck, I had some doubts while driving to my garage this afternoon to try the Corvette/Impala disc brake retrofit. Here are the results after fitting the parts together. It worked! I never imagined that Corvette rear rotors when fitted to old Impala hubs would work as a substitute for the original obsolete Impala rotors. Words can't express my appreciation and gratitude for your innovative suggestion! You saved me at least $200.00 and the many headaches of tracing down obsolete parts. Once I install this mess onto the car, I believe each front wheel will be positioned about " outward since the Impala hub is mounted to the inside of the Corvette disc. Originally, the Impala hub was mounted to the outside of the Impala rotor so the difference is the rotor thickness in the hub area. Unfortunately, this is the only way to mount the hub onto the Corvette rotor. It should not be a problem. I thought your idea was so nifty I took a few pictures with my digital camera to show the retrofit.
The above picture shows the original obsolete rotor This picture shows the Corvette rotor next to the Impala disc hub
This picture shows the Impala hub mounted to the inside of the Corvette rotor. Temporarily, I got regular bolts holding the two pieces together. Latter, I will install wheel lugs.This picture shows the Corvette rotor and Impala hub from the backside as well as the Impala spindle assembly.
The following pictures show the everything put together for an initial trial fit on the workbenchDifferent angle of the completed assembly
Different angle of the completed assemblyDifferent angle of the completed assembly
Different angle of the completed assembly
I must also add that I appreciated everyone else's input on my original thread, Post # 97572 on the Rodding Roundtable Forum

The only part that was purchased was two rear rotors for a 1968 Corvette. As per the parts book, the rotor fits 1966 to 1980 Corvettes. The rotor part number as listed my manufacture is Bendix 141213, Raybestos 5501, Aimco 5541, and Midas BR1208. The original wheels lugs can be reused. The only drilling needed is slightly enlarging the lug mounting holes in the hub to accept the sholder of the wheel lug.
I must confess I have done the same thing in the past. I knew it would work with a 68 hub as the spindle is the same. I Found this out trying to come up with 12" brakes with a 4 3/4" bolt pattern.

A couple other interchanges that are not listed, A S10 rear drum will fit on a 60's Chevelle rear end, and costs less than 1/3 what the Chevelle drum does, and 60's Mustang drums will fit a Maverick rear brake, and again cost less than 1/3 the normal price.