I purchased a similar bike from italy - and was told the following info in spanish:
Hola, de ese modelo se hicieron en dos cilindradas de 230 y 250 cc son exactamente iguales, se hicieron básicamente para exportación y casi todas fueron a Italia, no hay cifras de fabricación, pero no creo que se hicieran mas de 200.
For me the bottomline a limited run of 250s have been made late in the run for Italy for Tax or whatever reasons.
And I have full road docuemtents that say it is a 76 with 250CC.