Weber air cleaners on a V8 engine do not last long. What happens is that the natural fuel reversion soaks the filter element and will catch fire on a restart.
Generally speaking you never use filter elements on 48ida's on a V-8. It just doesn't work.
Use screens and since air flow restriction is a function of surface area, try to maximize the screen surface areas.
I have a bunch of friends running them on 289 Cobras. One of them ran them without screens on his Cobra which he drove regularly for 28 years without anything on the stacks at all.
If you notice, the Group 4 factory race cars that ran Webers used extended velocity stacks that wound up around 5" high in total. That did two things. One was to change the torque curve of the engine somewhat to make using 44mm "auxiliary venturis" more useable and 2) it kept the "cloud" of fuel vapor within the velocity stacks rather then having it wonder all over (for the most part anyway).
It is possible to limit the reversion, but not to completely eliminate it with revised cam timing. Jim Inglese initially experimented with that and basically for the Cleveland there is one cam, a hydraulic lifter one still offered by CompCams that they refer to as the "Weber Cam".
The problem with that one is it doesn't entirely eliminate the reverson and it kills around 100 hp that ordinarily would be available in a conventional longer duration, bigger overlap design.
The magic number with a Cleveland and dealing with reversion is limiting overlap to under a total of 28°. If you look at the timing specs on a stock Ford CJ cam, the overlap listed is right there at 28°. So some guys still running that cam and adding Webers have no idea WTF I'm talking about with either the reversion or air cleaner issues.
"C'est la vie", say the old folks. It goes to show you never can tell- Chuck Berry. 
