Catalytic converters were note used on 70"s rv, my 79 has EGR but don't know if a 77 had one, if its missing one just buy one any where and stick it on and put a vacuum hose on and put vacuum hose under wires to hide, it don't have to work to pass it just has to be there, mine is frozen, wont move so I plugged vacuum hose, it still runs fine no problems and passes emissions test fine.. I don't plan to buy a new if I don't need it.. also put a 1/3 or more of E-85 fuel in your tank before emissions test and drive it till its warm and you should pass test without a problem...
