pretty sure the 340 and 383 base plates are 3/8" in height diff. just traded with mike ross .. he was careful to be sure it was in fact a 340 plate I had ... the adapter looks like it is about 3/8" to me ? just a thought ..
When you say "base plates", I'll assume you mean the actual Shaker base/carb plate", and the adapter you saw? did you have it, or Mike Ross?
