The opening is cut out perfectly. Using a #38 drill (.101 inch) my meter came with 2 small screws and nuts. So just drill two holes and bolt it in place. Look at Grainger, thats where it is sold. Or Amazon, as they hang on that site too. Cheaper ones on Ebay.
My meter came with the harness and screw and nuts. The cheaper units won't have the wire harnesss. I cut the scag harness were the plug was and using the plastic wire nuts I reattached the wires. 10 minute job. Mine came from Amazon
Hour Meter, DC Quartz Hobbs part number 085094 44