does this mean you are going to use socket head studs instead of screw type like the originals on the primary cover, if so I would suggest you use a screwdriver that takes hex bits and just tighten as you would a screwdriver unless your real name is Dan and you like cow pies.
The gearbox outer cover is not likely to warp but you could strip a thread if you got carried away with the four nuts, ( replacement studs are readily available), I just go by feel on these as they do not need to be over tight to seal the gearbox.
Millions of years of evolution have given you a body linked to a brain in such a way as to be very adept at measuring by feel - trust yourself and Darwin wink2
All the best - Bill
