I'm trying to work out my transmission tunnel from the book, the rear part of it I'm not sure it is right, the book isn't clear , can any one measure theirs please, it looks like the dim is 85mm to the outside of the rails but I think it should be inside?

I can't help you with the measurement as I had to change mine for the MX5 donor, but don't forget the top dimension is larger than the bottom one because the seat back is at an angle. You're basically looking for the top bar to be in line with the bottom bar so that when you come to add the panel it's still vertical.

I was thinking that would be the case, I think I will just work it so it matches the bottom

Treat the book as a guide and place the engine and gearbox in place then build the tunnel around this, try and make as much space as possible for your feet as the footwell is already constricted so any extra space you can win is bonus.

If you are going to track it and mostly drive solo think about moving the engine and box over to the near side a little to balance your weight.

I would allow no less than 20mm space wriggling room unless you plan the really tie the engine and gearbox down hard as they move around more than you would think.

Regards Mark

Still would like to know the dims for transmission tunnel top on a factory chassis, width at rear overall and width at the uprights at front of tunnel
I'm trying to work it out but nothing seems right

Cheers all

Just been out to measure it.
At the rear of the tunnel on top from outer edge to outer edge it is 118mm.
At the front the distance from outer edge of upright to outer edge of upright is 273mm.

HTH
Ian