The face and where the needle is installed is the difference. I bought a early style removed the needle install the later face and put the needle on a zero. I also went the other way. late to early and very easy to do. I just bought an 8000 repo tach put a replacemen face on from Classic. It ended up looking an working perfect
Below is what we started with off Ebay. Repo 8000 off ebay and it will work with MSD or any after market ignition . Unlike the old factory tachs that burn out it is digital