Well, first off, the R-13 designation was not used until 1955 at the earliest, so if its early 50s then it wouldn't be an R13.
The Buffet models prior to the R13 don't seem to have a "real" name, rather they are often advertised on eBay and other places as the so-called "Pre-R13"
First off, is it marked Made in France? That's the minimum requirement to be an R13