"Replica" had a different meaning in those days. It just means that it duplicates the specification of the car that set records on the Bonneville Salt Flats. It doesn't mean what we think of today, that it is a copy of something, but not a "real" one.
Interestingly, this first-chassis-but-fourth-completed 100S did not originally come with that "replica plate" that the other 100Ss had, but someone either found an original or made a very nicely patina-ed copy and put it on the car anyway.
I wrote the catalog description of this car, which you'll soon see on the RM website. Look for this car to be on the cover of the March issue of HEALEY MARQUE magazine.
I echo HealeyRick's comment: not sure why anyone would call it "infamous." There's nothing shady or negative in its history. It was delivered at actor Jackie Cooper at the 1955 Sebring race where he co-drove it. A wiring problem caused it to quit short of the finish, but Cooper pushed it the last mile over the finish line so that it was shown as finishing the race!
It is, in my opinion, a very desirable 100S among 100Ss. The pre-auction estimate has it selling for $1m plus or minus. I'll be surprised if it doesn't go for more than $1m.