Very true, poorboy racer!
40 or 45DCOE webers (side-draft) can be fitted without cutting the firewall, using a short inlet manifold (3 inches tall) and short sub-stack ram pipes inside a K&N filter. HOWEVER fitting a weber to your mini is not always a case of whether it fits or not.... you could end up losing power if the setup does not tune properly with your engine... You'll find that changing the ram pipes will alter the power. Changing the BRAND of inlet pipes will change the power - even if it is the same size!!
Usually, longer weber inlet manifolds help produce more power (and reduce dash space!!)
As for downdraft, i agree too, the 28/36 DCD weber is a reliable little unit, and the setup wont squeeze under the bonnet. SEE PIC BELOW (FROM MINIWORLD ISSUE #1) I guess you could cover it, or use a flatter filter......
Its all about getting the AIR FLOWING. Shop around a bit, i'm sure something will work for you..