Don't worry about the levels, they're of limited value. For architectural work, they're useless - use a gridded groundglass. My 4x5 has a round bubble level, which is accurate, but I've never used it. My 8x10 has no levels and I've never missed them.
Just get the levels as close as you can with shims, use them as a guide to get the camera close to plumb and level - the final arbiter is the GG anyway. You only get a flat and level horizon at sea, anyway.
So ignore the spirit levels you say? Or just get them somewhere close enough? :-/