Welcome aboard Ed. Great to see another TR3 guy hop on the band wagon.
Removing the tunnel is pretty straight forward, and as others have mentioned, the biggest problem is rusted screws in the captured nuts. All of those nuts can be accessed from underneath and on the firewall, so several application of penetrating spray should make them movable. The two products that seem to work best is PB Blaster (available at most auto stores like Pep Boys) and Kroil, which I had to buy online. WD40 just doesn't do much in these situations.
BTW, why are you removing the tunnel?? Clutch time, or are you just starting a frame off restoration? Inquiring minds want to know. And we require pics of everything! :laugh: