So is mine... it was quite common when the S3 came out for people with S2a's to change body bits around to make the older S2a's look more modern.
I also expect if it was being re-built things like the S3 bulk head was put in.
Still don't think it's that dodgy. not compared to the usual tax exempt series which just so happen to have had every single component replaced to make them look like a 1998 90.