Cool idea. I am looking forward to this build!
Random thoughts and useless trivia:
You could add scoops to the window cutouts in the sleeper and duct these into the engine inlet.
Installed with the original nozzle configuration, the front nozzles could be pointed slightly "up" at speed to help offset aerodynamic lift and keep the front end planted. All 4 vectored up and forward for braking at the end of a run
Thrust from the front nozzles of the R.R.Pegasus is made up of bleed air from the fan section at the front of the engine so it is much cooler air than the rear pair whos thrust is generated by combustion gasses,