from the reg its a 2a but dash looks like a series 3
It's advertised as a Series 3, but they weren't built until 1971. Wings, bulkhead, dash, rear crossmember, radiator panel and grill, steering wheel are all Series 3.
If I was cynical I would assume that the only part that is not S3 is the 1966 S2A registration plate, which someone may have just stuck on to gain tax exemption.
However, it could have been a rotten S2A that has been completely rebuilt using series 3 parts which would be completely legitimate as long as the chassis is from the Series 2A vehicle. I do have my doubts though as does the seller with their incorrect details in the advert.