85 hydro boost to 74 would need little mods.
power steering hoses are oring seal style.
74 is 45* seat style.
and i think brake line nuts / master threads are diffrent.
and if removing vac/assist brakes will need to modify the stud/bolt arangment on the brake pedel suport in the cab. and brake pedel might have the diffrent hight hole for the brake rod to clip to than vac/brakes.
but other than this its a bolt in.