Winnabago cheiftan needs help i have a 73 24 cl that is all orignal id like to keep it a shes got a few issues 1she has a 4 inch serwer outflow

Hi   im in need of some knowledge on my winne yes shes a 73  24cl. Im second owner. She was used verry litt.e before being barn kept n tarped since 74 i got her last year    wellshes orignal alright  right down to 4 inch sewr outflow  butdidntcome with 4 inch adapter   how tofix  make it standard 3 inch.    Next is  range need a coleman holiday with the top oven   or complete oven/pilot knob assembly and knob id really like to keep the top oven idea   ok next is my fresh tank its steel n rusted thru how to take it out without tearing the house up  aney ideas or infoisgreatly appprecated thanks