As an option if you just want some basics or add-ons like a clock, max/min, additional trip computer etc you can use a bicyle computer that allows a high speed range such as the Sigma Sport line.
It's a cheap easy way to add digital spedo if you've modded away from the mechanical system. I have one that started as a BC800 and I re-packaged it to put the buttons/battery in one box just in front of the ignition and the main unit above the gauges without it looking too much like a bike computer. I mostly like having a clock in view but the max and average speed and trip counter is a bonus (I use the oem trip counter as my fuel gauge as I expect most of you do).
This is an old picture, did this in about 2003 or so and it has held up great and cost me all of about $20 at that time.
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