Seen and had hands on both round doors and Sq door 1980 DF Models also seen & had hands on 1981 round & SQ. door DF models. As well as 1 Non DF model 1981 My friend has one which about three years ago I asked Chris about but he did not have any info on it as well as a few more units I ask about. The EFM records are incomplete .
The earliest DF Model I had my hands on was 1979 round door 2 of them But Just seen a 1978 DF Model for sale .
I believe by late 1981 all 520 DF units where SQ door . The 1980 & 1981 year models came both ways they must of had left over parts.
My friends 1981 Round Non DF puzzle me as well as many other's I have talk to The only thing that makes any sense that it is Kirkland boiler top That might be the reason for not being a DF model Only ever seen 3 Kirkland boiler tops .
Who knows Not the first time EFM made or changed things out of the ordinary .