The āS4ā is a right old bitsa (and an S3 body?), the Sprint is a chopped coupe with a Spyder chassis. Neither for the purists I would have thought.
The auction narrative on the S4 states that the car when owned by Pat Thomas in 1974, had the bodywork modified for competion use, which accord to them the arches were part of that change. It seems also that Pat Thomas was looking to change it to more like a 26R, which may account for changes to the front. It could be possible that for use in competition that wider wheels were fitted which required the arches to be modified. The wheels in the photograph certainly appear to be wider than standard. Also I find some of the description in the first paragraph of the auction house details a little confusing and perhaps inaccurate.
I not also that it is described as a 1970 with a āJā registration, yet in the Listed Specification it was manufactured in 1969, yet the chassis plate sugests a mid 1970 build. All of which would need further investigation and verification.