Matt

Have a look at the pic, from the centre of the crank to the flat area behind the engine is 50mm to the top of the fibreglass belly pan its 90mm so this makes the belly pan 50mm deep because there is a 10mm fall on the flat area towards the engine bulkhead, the only problem I can see with what you are proposing is possitioning the battery to get the correct cofg may not be a problem if your engine is heavy enough, I had to put my battery right behind the belly pan front vertical to ballance without weight.

Hope this helps, let us know how you get on, and post some pics of the mods.

Mike