Aftermarket tach in rally cluster 67-71

Looks like a nice clean install. I'm thinking about doing this as I may have to pull the cluster to change my dash pad. I should have done it last year when the whole dash was out :BangHead: (the idea hadn't even crossed my mind). Do you know what the id of the tach plug is? I assume the tach face is slightly larger. I was thinking about the Autometer 3780 (if it takes the 3 3/4" tach) as it goes to 8000 rpm. Thanks.