Kelsey-Hayes caliper upgrade

K-H calipers are fixed mount while 73-76 are floating, either pin of slider mount. So no, they won't physically interchange. You wouldn't gain anything if they did, they are just as heavy, more complex, and the pad area is not much greater.

If you want to increase pad area and shed unsprung weight, I believe there are Viper caliper adapter brackets out there. Try Dr Diff. Your biggest bang for the buck would be changing to the late B-body 11.75" rotors.