Based from my own experience dealing with these companies:
1. Stay away from Seattle Speedometer. Please check their Better Business Bureu complaints.
https://www.bbb.org/us/wa/ellensburg/profile/gauge/seattle-speedometer-llc-1296-22822216/complaints
2. Nichols Speedometer & Instrument both did excellent jobs with reasonable price on both my 964 and 911 3.2 gauges. Note: they don't do modification on dial faces just repair.
Seattle Speedometer messed up my gauges and still charged me for it. I had to send them to NSI to have them repaired.