Check with Bob Farr, he posted in a thread from someone looking for a 5/16x14...and I could be wrong, but I've never heard of a Meucci with a 5/16x14 thread...unless it was specifically made with the different thread size.
Trying to be helpful...but sticking my nose in where it wasn't asked...
I have a ob-1 and a g core that will fit your meucci. I will bump them to the top and you can look at them or send me a pm with your e mail address and I can send photo's. Thanks