Lachie_82
I understand that the standard offset is 12p so what I can gather is that this wheel will sit a further 6 mm out from standard offset.
Using the figures you have quoted, and assuming you are referring to a 6x13" with 12p wheel as the starting point, the new wheels have about 7mm less inside clearance, and extend a further 19mm.
See:
The cited size and offset of these wheels suggests a wheel backspace of 4.25" ( which I think is about 1/4" deeper than an Escort 5" steel wheel and optional 5.5" alloy "Volante" wheel. I'd be grateful if anyone owning a set of these 4 spoke replicas could verify this and perhaps even post some photos of them fitted.