Mk1 tunnel with a pronounced hump on top of the tunnel in a large removable panel round the gear lever: (MGBs Made in Australia)

Non-OD on the left with the lever at the front of the oval rim ring, OD on the right with the lever at the rear of the trim ring: (Clausager)

Mk2 tunnel is wider with a flat top, with the lever in the same position on both OD and non-OD: (Clausager)

Mk2 has a small removable panel HZA1431 screwed to the tunnel:

Removed - suppliers show gasket AHC188 under it and I did find that on a 78 sitting on the metal tunnel but both Bee and Vee have thick insulation there which makes the gasket pointless:

Mk2 with the 72 and later centre console and arm-rest/cubby. What the rubber bit at the top of the gaiter is I have no idea, it came with the car - possibly hiding a bit of rattyness at the top of the gaiter, but like steering wheel and the gear knob it seems churlish to replace that part of the car's 'character':

With that the tunnel carpet can be cut to allow removal of the small access panel without pulling the carpet back, saving a section of carpet to drop back on top for noise insulation:

A 4-synch gearbox can be installed in a Mk1 car but the large removable panel on top of the tunnel needs a section inserted to move the hole back for the 4-synch gear lever, as indicated by the arrows: