Removable brake arch
I have an old ALAN aluminium frame i bought recently, and i was taking a look at the rear brake arch noticed that it was screwed in on both sides. Now, i'm sure it's glued too, but if i heat it up a bit and take it off, will it really affect the structure of the frame?
Also, does aluminium reacts differently to steel when exposed to a naked flame?
I can start an answer for one of your questions. Aluminum is a different animal when it comes to the 'naked flame'. When it reaches a certain point it will just fall apart. I have not worked that much with it so the other guys on here will have to explain it in more detail. If you have some 'scrap' around you could do a 'when does it melt and fall apart test. Good luck on your build.
Those old Alan frames (tubes bonded into lugs, right?) are SUPER flexy. Normally, you could take out a bridge without making a big difference- but on that frame, it might end up being a prblem.