Back when I sold 3020's new I don't remember any 3020's that had different CID engines for only 2 years. Granted later 3020's were advertised at 70 pto HP instead of 65 pto HP as the first ones. Late model 3020's were built from '69-'72' Tratordata lists 227 CID for gasoline/LPG & 270 CID for diesel. The earlier 4 cyl. engines could have later model cylinder liners/pistons installed to increase the CID. The same basic Waterloo built 4 cyl engine was used from '61-'72. Which fuel does your engine burn?
Update. I just viewed the JD parts catalog #1115 and it shows a 4" bore(fits block #R26150) & 4.25" bore liners fits all the later blocks.