The pit installation will involve some necessary lifting gear for
every time you want to access the engine for major servicing. This seems
like a ball ache to me because of the need to disturb fuel lines, exhaust
pipes, cooling pipes and cables every time you lift the engine. Have you
worked out how you are going to do something as simple as a lube oil change?

Having dug a suitable trench for the mounting block for my SoM, I can tell
you that pit-digging is no fun. You would probably need a pit of internal
size at least 1200 x1200 x 1200 deep, they you have to brick line the walls
and pour the mounting slab. This seems like just too much work and little to
be gained. Bear in mind that an acoustic cover can be made from £60 of
plywood and a bit of rockwool.

Lister suggest that you mount the engine on a pedestal (about 150mm) above
floor level to make servicing easier. I tend to respect their 85 years of
practical experience and better judgement.

Just bear in mind the level of the water table in your area. It was not
uncommon for the pits dug in private garage floors for car servicing to fill
up with water. It will certainly very quickly become contaminated with oil
and water.