Yeah I have been concerned about those front plates getting bent and thought about using the wheel bulkheads but as you say then it looks like 520 clone, here are some images without the drum to give you a better idea of how it works:



There is a large titanium axle at either end 40mm diameter with a 16mm hole though the middle, the drum spins on bearings on these axles then a 16mm rod made of either titanium or aluminium goes all the way through the centre, each end has an M8 tapped hole so a bolt goes from the outside of the hardox armour into these holes, the idea is that this should tie them togather so they are less likely to be pulled apart and also acts as a spacer to stop them being pushed together.

I have been thinking about making it less tall but it would mean I would have to machine down the flat bar used to make the chassis unless I can get it all the way down to 60mm as I am currently at 3" so it is quite a large step down but may be possible, could mean reducing the drum diameter as well which will mean smaller bearings and so a smaller shaft going through the middle but could save a lot of weight.