i've just MOT'd my classic. I did all the sills and inner wings and had no probs, these were tested with the testers hammer. Also no probs with leaky exhaust (slight) or with leaking swivel seals either. The main problem is that if rust, any rust, is within 30cm of a structural point of stress or a seat belt mount, then it will fail. If you had seatbelts fitted and remove them prior to MOT then you cannot just put them back in afterwards as they have not been tested for safety. Also unless the tester is registered blind, he will see the mounts and know you have removed the belts. If the mounts are rusty, removing the belts will probably destroy the arch anyway so irrespective of whether there are belts fitted, you will fail likewise with the outer sills. It isn't a big job to do the arches, i did mine by cutting a 6" square out and replacing with new material, full seam welded, drilling afterwards and placing 2 off 2" square galvanised plates (B&Q) 1 either side of the arch before fitting the bolt. No problem whatsoever from the tester and with me replacing the entire braking system, new exhaust, and all the welding, he thought i was crazy spending so much money on an old vehicle (1985) One plus point is that there was no emissions test due to its age so i didn't worry about this. One other point about removing items before an MOT, I had an XR2 and removed the rear wiper as the rear window washer was faulty, the tester then said it failed as these parts were fitted to this model and should be present (he had an XR2 himself). Anyway, good luck with the test
Jock