The original cold air box was attached with bolts. Unlike one replica version of the CAB that apparently uses some form of nutsert fixed to the aluminum box, the originals had a metal plate with welded nuts that was riveted to the inside of the CAB. I have seen that Sports and Classics (NFI) sells a replica that uses this OEM style mounting. The OE style would definitely not allow fitting of any sort of velocity stack. The "other" replica could probably be modified to allow use of the Low Profile Velocity stacks without too much trouble.
It would be very easy to fit studs to an OE CAB, although that might actually make it harder to get all 4 lined up at one time. I have considered doing this on several occasions.
Currently my CAB is on the shelf awaiting some crack repairs. In its place I have fitted the low profile velocity stacks inside a pair of Lynx-type foam filters. Hope to find out shortly how it runs and sounds with this setup.
Ignoring the fact that my engine has a couple of extra cylinders (and 3X the openings) that's pretty much how this
unified air filter housing & low profile velocity stub-stacks are attached. The Webers already have studs in them (5 or 6 mm dia./nuts are 10 mm across flats, and requires a highly modified open-end wrench to access them). Standard Weber rectangular x 1-3/4" high filter elements straddle the stubs-stacks, and a stainless steel panel slips in to secure them.
I made the box a 2-piece design in the likeness of a 100M CAB, but it would've starved the engine of air without the added holes in the ss panel and the box itself.
Test-fitting the cover, before holes were punched. Hard to describe, but with slots in the top of the box, it slips inside the opening at the ends and bottom for a very secure fit, only requiring screws along the top (had to be able to remove/replace cover for filter maint.).
Holes were cut with a Greenlee 1/2" conduit K/O punch (7/8" dia.) and then belled with a punch & die a machinist friend made for me.