Updated rear brake calipers on '67S

I am in the process of installing an '89 Carrera front suspension on my '67S. I would like to also upgrade the rear brake calipers, preferrably with Carrera/SC units. The narrow bolt spacing won't even allow me to install my '67S front calipers on the rear without modifications. Anyone had experience in dealing with this problem? Who makes adapters to retrofit newer calipers on the early S vented rear rotors? Thanks for any help you can give me.