I can't say if they moved it between '75 and '77, but my '75 service manual shows the 27' Univolt on the curbside in the rear bath. The diagram isn't particularly clear... I don't know if it's accessible from inside through a panel between the tub and the wall, or if you get to it from outside, or if the diagram is just crazy.
Il Carriaggio — 1975 Argosy 24 | Il Progetto — 1976 Argosy 28 Center Bath | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill