Going boeing - the 737-400s have the EGPWs GPS and old (albeit SMITHs industries) FMCs capable of integrating the GPS signal - only (apparently) CASA would not allow them to connect them. Even if the old 767s FMCs were updated, would they run into the same problem with CASA, or would dedicated GPS for FMCs need to be installed.
(Personally I have no idea about the system integration of EGPWS GPS input vs normal FMC GPS input)