If your worried, use nyloc locknuts (or similar) and chop the rest off.
Out of interest, is there anything between the angle of the plates you have welded in (under the top 2 bolts in the pic) as that looks like you could crush the angle by doing the bolts up tight/they might settle over time and come loose. Im presuming you are going to weld ends onto the plates too judging by the way you still have your earth clamp on? Im also presuming you have something similar on the underside of the shell?