Dave;
The engine I have is a .45 according to the specs I found on Scepter Flight, but the mounting bolts measure the 1 1/16" center to center. the width of the base is 3/4" , length is 1 3/8" and is 3/32" thick. This is a cast piece. I can email you a photo of the engine and spare venturi I have. If Jim can't get you fixed up let me know, but I'll bet they all used the same foot print for mounting from the .45 up to the .60, knowing how "frugal" Duke was.
Type at you later,
Dan McEntee