40x40 matrix :lol:..... yep, its a pi**er.
iv done the same with the bosh rethrox cad files... im also buying from Valuframe (just down the road for me)
my ballscrews have just turned up so im on with fine tuning my drawing to fit them
im using the Valuframe 200x40 profile for my gantry sides.. i cant see plate performing anywhere near as well without some sort of buttress
the only real fear i have with the profile is trying to drill tidy holes for the Y screw, not looking forward to that one

sooooooooo..... in responce to your ali or plate dilema...... crack the base to gantry interface and profile looks to be the option for limited tools.... if you can handle the cost of heavy profile... im looking at a £500 ali bill, thats including a 20mm slab for the cutting bed, sounds a lot but should go together with an alen key :)