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Saddle height
As with so many things in cycling fashions have varied, but there was certainly a time between the wars when it was normal to have a small frame and a lot of seat post out.
I'm fairly sure that the s/post on this bike is original, so that suggests that it wasn't unexpected to have a lot of it showing. Looking at pictures from the period it certainly seems that although utility riders would often have their saddles flat down, the racing men did not.
Here's a picture from Cycling for October 1924:
I would have thought it would have had a much shorter rider back then. The fashion was for much less seatpost showing so it must have had a more upright ride than how you have it for your legs? With the saddle down it looks like a pretty conventional riding position for a shorter gent.
Intrigued to see what you do with the brake. I don't know if it helps, but you can get inline cable breakers from SJS Cycles. One could fit either on your straddle cable or there might be space just before it:
https://www.sjscycles.co.uk/cables/jtek-cable-splitter-for-gear-inner-wire-black/
https://www.sjscycles.co.uk/cables/jtek-cable-splitter-for-inner-brake-wire-short-black/