Re: Aluminum or Steel? Which do you prefer?
I see whatcha doing now & I agree that specific application is prolly acceptable... but I dunno if I'd recommend it to others as it's a lil dicey unless they really understand what the consequences may be.
Squishing tubing is a chancy game, it'd not take much to fracture or even dent & compromise it's integrity, particularly with the bikes most commonly motorized & folks unfamiliar w/the ways of metalworking...
I see now you accounted for some of the things that worried me, like galling (ya used a C clamp w/uniform, slow pressure) and fastener side load (tubing expands, breaks engine case where studs are) by adding an extra rear mount in the front as a standoff.
It's far from ideal what with pressure points instead of a nice solid contact & while it's completely acceptable to do things like that w/yer own bike as you'd be familiar w/it... I'm not so sure I'd be comfy recommending it instead of an oversized mount or selling it as a finished product...