Yes, it is. The biggest are S&S Cycles and Revtech.
I owned a Big Dog Boxer, but can't recall which engine it used, It was about 1700 cc though.
I also customised and re-engined an FXR and may have used a Revtech in that. Again it was 17/1800 when the stock engine was 1400 as I recall.
This was all between 15 and 20 years ago and the amount of aftermarket engines and engine parts available was staggering. I recall ordering from the Custom Chrome and other catalogues which were stacked with every part you could ever imagine for Harleys and Harley styled bikes.
It seems amazing that an engine that only went out of production five minutes ago is so difficult to get parts for.
