I already had a large access panel in the side of the bulkhead and thought that with my extra one on the top I would be good to go. Alas no! There is no way to get a spanner on the top clutch m/cylinder bolt without cutting yet another access hole! Why Marlin didn't just have a complete removable top panel over the whole area beats me. If it was thick steel and the edge of the "hole" was reinforced with extra angle to take a ring of captive nuts it would be plenty strong enough.
For anyone else doing this job remember to fit the top m/cyl bolt to the flange before fitting the banjo fluid connector as it won't go in afterwards!