Why would someone 'hammer modify' the RH rear fork? I think a second owner wanted to fit a double or even a triple chainring to a frame built for a single chainring (as previously discussed). The fork had to be dinted in to allow for the extra chainring(s).
I think it would be fun to re-birth this bike as a 90's time trial bike as previously discussed. It also weighs in at a very light weight. The aero rear end, the internally routed brake cable, etc, all add up to a time trial bike with a single chainring. It would be nice to see just how light you could make it.
A set of cow horn bars fitted to a long stem to fit you together with a clip-on aero extension bars would look great. You could even go 'old school' and fit a friction gear change lever to the end of the aero extension. The friction lever could also be fitted to the existing gear lever boss. The seat could be 'jacked up' to suit your height and really enhance the look of the bike.
A bike a bit like this but with a rear derailleur:
(I could have picked a nicer looking example)
Greham Obree's TT bike.
Old school clip-on aero bars with bullhorns. You could fit one gear lever. If it was my bike, I would have the rear dropouts re-set to a 126mm gap and fit a 6 speed 'corncob' freewheel (12 to 17 teeth) and a large front ring, say 53/54 teeth just for the fun of it. I would be looking for top-end speed on a flat course plus weight saving thus the corn cob 6 speed. I would fit the friction gear lever to the down tube boss. You would need a long seat tube - be careful as alloy posts can snap.
Best of luck - a really fun project.