engine clearance

[BenBrooks]

I'm thinking that I need to move my engine up a fair amount as i have next to no ground clearance. unfortunately, my bellhousing is getting very close to the bulkhead front crossmember. Question is, is 11mm clearance between the top of the bellhousing and the cross member enough? Or should I go to 21mm? I can't go more than this without moving the engine forward slightly (remaking the engine mounts) and/or shortening the sump as I have to clear 100mm ground clearance.

cheers

Ben