After the Chinese fuel pump fiasco, I'm leery of any new parts. I was leaning toward buying the new guts from one of the usual suspects and installing them in my housing.
Instead, I'm going with Kevin's choice and buying one of Jim Carter's rebuilt units. He said that they've sold over 2000 rebuilt speedos and only one was returned for a problem.
He sends them out to somebody for rebuild (probably Then and Now, hahaha) and won't send you one off the shelf until he receives your original core. $341.00
I bought some 10-32 wing nuts to use for re-assembly. It's easier to get my fingers in there than it is to get a tool on a nut, even with the radio grill removed.