74 hilux 5 speed

I recently aquired a 74 hilux with the 18R engine and a 4 speed. First, I know the 20R and the 22R arew interchangable, is the 18R as well? second, Will a 5 speed tranny from a 20 or 22R bolt to the 18R? (I guess thats kinda the same question) New to Toyotas and don't have a clue.