On Dec 18, 2016, L. Christiansen in Brabrand, DK, Denmark wrote:
"I was about to replace the clutch lever boot, but ran into trouble. The new boot is a very tight fit on the lever head where the clevis pin resides. This one I can manage. -- What really bothers me is that the space between the inner and outer lip where it fits the bellhousing is way too narrow, about 4 to 4,5 mm. The wall thickness of the bell housing as about 7 to 8 mm, so the new boot will not fit. My MGA is MK-II 1961, originally fitted with the twin cam gearbox".

I replace the clutch lever boot regularly on lots of MGA. Seems like everybody needs a new one, having been exposed to oil and neglected for a long time. This is easier done on the workbench with a gearbox rebuild, but can be done in situ as well.

The first trick is to grind the sharp corners off of the square input end of the lever. Chamfer the corners, or round them off to make the lever end a little less square, rounded off to be smaller across the corners. Then use a new boot, and be sure it is not cold. It doesn't have to to hot, just warm to the touch. Put dab of oil or petroleum jelly on the inside of the small hole, and go ahead and push it over the lever. A new boot will stretch a lot without damage. (An old boot would likely be destroyed when it was removed).

For the flared end, start by pushing the thin web edge through the slot beginning with the upper end (where it is more difficult to reach). Then work your way around the sides, finishing at the bottom end of the slot. The final push will be to use a blunt edge blade instrument like a plastic spatula or a screwdriver that is not too sharp on the edges to push the last thin edge of the boot into the slot. Massage the boot a bit to get it to relax and settle into final position.

The slot around the base of the rubber boot seems to be a perfect (tight) fit in most gearboxes. I don't recall doing this for a Twin Cam gearbox (often used in the MGA "Deluxe" cars with the Twin Cam chassis). As Christiansen noted above, the Twin Cam type gearbox may be thicker in this area of the bellhousing, making it a bit more challenging for final seating of the boot after installation. But in the end it seems to work okay (once you have muscled your way through it).

Now just to add a bit of confusion, apparently the Twin Cam type gearbox (also used in many of the "Deluxe" cars) has a thicker bellhousing in the area of the clutch release lever boot. But they all use the same part number for the rubber boot. This may provide some additional challenge for installation of the boot but apparently it can still be done with a bit of persistence.