Every .303 sporting rifle that I have seen from that era has the same rear sight. Fixed, folders and a ladder.
These rifles are not conversions. Factory made sporting rifles. Like Ross sporters, some parts are shared with service pattern arms.
Handloads with Woodleigh 215gr round nosed bullets loaded to Mk. VI velocity would be appropriate.
I have a BSA Model 4 sporting rifle. Sort of the poor cousin of yours.
In 1900, these were very modern sporting rifles.