Going by years :
1965-1966 - In the U.S. no C body Dodge offered a slant six prior to 1970. The 318 was optional on the Polara 318 sedan while the 383 was standard on the rest of the Polara, Polara 500, Monaco and Monaco 500 models. In Canada the base engine on all C body Dodges was the slant six and the 318 V8 optional for 1965-66. Interiors of Canadian market Dodge C bodies used Plymouth designs (with a couple of exceptions - door panels on the Canadian 1965 Polara 880 and Monaco for one.)
1967 : In the U.S. the same base engines as in 1966. In Canada for 1967 and 1968 the Monaco 500 had the 318 V8 as base engine and the rest the slant six. The US Dodge instrument panel was used starting with the 1967 models
1968-1969 : In 1968 and 1969 all U.S. Polara models had the 318 standard, all Monaco models the 383. In Canada the standard engines for 1968-1969 were the same as 1967 with the 1969-only Monaco Brougham having the 318 standard. The Canadian 1969 Monaco 500 used the same exterior trim as the US Polara 500, although with Monaco grille and taillights
1970 : In the U.S. the 1970 Dodge had a Polara Special offered mid-year in sedan, 2 door hardtop and wagon, with non-wagons available with the optional slant six. For 1970 in Canada, the Polara and Polara Custom sedans and hardtops had the slant six standard and the rest of C-body Dodges were 318 V8.
For 1970 the Canadian C body Dodge continued to use C body Plymouth upholstery - Fury I = Polara / Fury II = Polara Custom / Fury III = Monaco / Sport Fury = Monaco 500. The optional Sport Fury Brougham interior was used as the Monaco 500 Brougham. Exterior trim was similar with the Canadian Monaco 500 using the US Monaco exterior trim and the Canadian Polara models using the same exterior trim as the U.S. Polara models.
1971-1972 : In Canada the Polara / Polara Special had the slant six engine with the Polara Custom and Monaco with the 318 V8. In 1971 all C body Dodges used basically the same instrument panel as the Plymouth Fury in Canada and the U.S.
Monaco convertibles were strictly Canada only - Monaco (1965-1969) and Monaco 500 (1967-1969). For 1970 only the US Polara series convertible was sold in Canada. As the Canadian Monaco series was priced in the same class as the American Polara, Chrysler Canada did not bother with a 1970 Monaco convertible and marketed the U.S. Polara in Canada - and as a Polara just to confuse everyone.
Hope this is at least a little clearer than mud.
Bill
Vancouver, BC