The disc brake set was identified as the TSM kit:

http://www.tsmmfg.com/1190.html

Apparently, it uses GM calipers and 82-87 Lincoln Continental rear rotors. The main problem with the kit is that the calipers hit the shocks on sharp turns. It has been proposed to switch the brackets so the calipers will face forward.

Also, the brake master cylinder must be checked for the existence of the residual pressure valve. A pressure of 10 lbs. is way too much for disc brakes. Instead, an inline 2 lbs. valve must be used.