[Roadsters] After market gauges for late model roadster?

[Tom PRATHER]

Hello,
   
     What is the correct size gauge that will fit the 2 larger opennings for our dash? It seems to be around 4 inches but many companies either sell 3 and 3/8inch or the 5 inch gauges. Is there a true 4 inch or so that will fit ours or are we dwelling into the custom zone? Would appreciate any inputs from those that have experience in this area. Thanks in advance.
     
            Tom