Mallorys are not going to work even with an extra inch. I mocked it up and tried today.
This is a Chevy Mr mallory that Bubba modified for me to use with a flathead. It is not fully engaged and definatlly will not work.
In this picture the Mallory is not even in all the way
as you can see its not going to work, maybe one without the tach drive might work
Here is the regular bubba dizzy in my daily ride and as you can see add an inch and the belt can slide under there.