1965 Dodge Dart 4d sedan, 225 engine, correct rims

Hi,

My car, 1965 Dodge Dart 4d sedan, 225 engine, automatic transmission.

I need a stock rim for the spare tire. My parts book have all the pages in the wheel section removed, so I can not find the correct part number.
And, even if I can look for the right size, 13"x4.5" and 4 inch hole circle there is supposed to be a letter too, for the offset. Does anyone know what that should be ?

Thanks for any help.

Best regards, Bill