not sure about the plates you use gary, but the one's i do and others i've seen are 10mm plate, then add a couple mm for gasket glue, so more like 12mm.
i personally tried every combo possible with both the std rb26 mounts and std rb30 mounts with different bolt hole combo's, and i found i could only use the rb26 mounts and there were only 1 set of holes in the block that lined up. i didnt however try redrilling the mount holes.
with the cf bonnet i had, the latch was about 2inches from latching, and that was with the gearbox on and bolted up inplace. i'm yet to try a std bonnet.
i was just going to get custom carbon to do me up a bonnet. maybe if i do that i can get them to take a mould so there's a ready to go bonnet for this