Aftermarket tach in rally cluster 67-71

One question… I just pulled the cluster and removed the blank housing. The od of the blank is about 3 1/8". Is that the diameter of the Autometer 3 3/4” tach face? I realize there is a blank gap around the circumference of the face. Also, the id of the bezel attached to the front is only 2 1/2". I'm assuming it cuts off the hash marks a bit. I just want to make sure I didn't miss something and order the wrong tach.