I suspect that the UCSTKAM 2,5KR is a Rossi mk2 clone. A Parra 15 diesel push/pull head should fit with just a little fettling. They're available from Parra for about 30 Euro. Actually the Fora 15 Junior diesel is a real powerhouse for less or about the same cost as an UCSTKAM. I don't mean to denigrate the achievement of diesel converting one of the latter with hand tools though. Nice work :-)