Looking good matey!
I like the tunnel solution as the only bit that was an unknown for me was how to join my gearbox cover to the tunnel i had made, so it may be worth having a play and fabricating a basic solution while you've still got everything apart as when the body is on you end up doing some superb contortions when 'fettling' the interior
Coming into 'classic' cars for the first time in years i also found Spitfire Graveyard to be brilliant as they always made sure i had what i needed rather than what i asked for, explaining the what's and why-for's along the way!