I know of 2 tachs recommended.. an analog Auto Meter "Jr Dragster" , and the Digitron stuff. Digitron has some kind of helmet mounted Wireless HUD display option. Other cheap tachs update too slow.. lag time on rev.
The flywheel
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Both of us, esp you probably need a scattershield.. they wrap the exterior of the briggs fan/flywheel cover with strap steel around the OD. An aftermarket flywheel seems mandatory on the smaller lawn mower engines where they can come apart at 5-6000. Ours may be made better but if it fractures it could be deadly. ARC wheels are about 1/2 the weight of stock, rev quick off the corners on the lightweight racers but we may need more weight, I do more so than you. No magnet/charging system is an issue.