I enquired about this yesterday, this was his reply:
"Hi,
The turbo is not converted to a ko4. It is an original ko4 (ko4-23). with a machined, flowed & polished ko3s turbine housing fitted to it. The compressor has then had a curved aliuminium outlet pipe welded to it so the unit becomes a direct fit for the ko3/ko3s turbos. The spec is identical to the AMO4,**04 etc type turbos.
Both units used had done less than 10,000mls and has not run or been fitted since conversion.
It was bought from the continent. It will fit direct to the Cupra, obviously a larger tip and a remap will be needed. I do not know what other mods are required I sold my car before getting that far."