Thanks for those suggestions. I forgot that I had done some of them (like cutting down seat post).
Brakes on this bike are more or less integrated (specially made TRP brakes for this bike). Brake cables are Power Cordz.
Stem on this bike is a proprietary system. No fork crown, expander bolts, etc. It's actually a very adjustable set-up, but also heavy. Trying to source a lighter stem from Felt but they don;t seem to know where to find one (and they make the damn thing!)
Already has ceramic BB - and will be adding special jockey wheels (titanium plus ceramic bearings).
Looking into Bont shoes (currently using a Sidi Ergo 3).
Front wheel will have Vittoria's 80mm valve directly attached to tubular. But could run short valve and remove extender instead.
Just as an FYI, yes I wear a custom carbon leg. It was actually the one thing that turned me into a champion as it reduced rotating dead weight at the pedal by about 6 pounds! A couple of pics:
Small but important gains can be made...
Brake calipers. Many aftermarket brands are lighter than Shimano.
Brake cables. Nokon, I-links, or similar housing paired with Power Cordz.
Bontrager cork brake pads. Super light and work really well with carbon rims.
Cut off as much seatpost as you can, leaving only what is necessary to safely clamp it in the frame.
Switch all bearings to full ceramic.
Alloy rear derailleur pulleys with ceramic bearings.
Once stem is properly positioned and tightened, remove expander plug and top cap.
Remove valve extenders from wheels prior to race.
Quick release skewers. Aftermarket ti skewers can be found sub-40-grams.
Use the shortest chain you can without fear of snapping it.
Run a single chainring up front if the course is a big-ring only profile. (With a chain catcher?)
Find lighter shoes what what you are wearing (rotating weight).
I don't know if you ride with a prosthetic limb, but I know a couple para-cyclists with some amazing custom made versions... lightweight carbon fiber and aero shapes. Pretty amazing stuff!
I can't think of anything else. Best of luck to you in London.