When it came, I wasn’t sure if the magnet that attaches to the main crank pulley could only go one way so I wired it up and passed the magnet over the sensor. Sure enough, it only works one way and I marked it with a sharpie to mount it correctly.
After scrubbing the main crank with a small stainless steel brush and some brake cleaner and rag, I epoxied the magnet and let it set for about a day.
Then I used an aluminum L channel to make the sensor bracket by cutting out a V-notch on one side and bending it into a 90 degree angle. I was worried that it might not hold under the vibration from the engine and epoxied the cut out piece of the channel into the corner.
This got mounted with a water pump bolt and the sensor hole was drilled out to be in line with the magnet.
I pulled power from the cigarette lighter with a tap:
The dash already had a hole from the aftermarket heater control. I trimmed the hole a little larger for the plug in the back of the display to fit through.
The display is meant to be inserted into a cutout hole, but I wanted to use 3M mounting tape instead in case this wasn’t permanent. I found that a small 1/4″ piece of plywood filled the back of the circuit board so the tape had something to mount to. I hot glued it on, cleaned the dash with some rubbing alcohol, and attached it with the tape.
Overall, this was cheap and took about four hours of work. The display fluctuates a few RPMs (+/- 4) and I’d guess that if the sensor were analog it wouldn’t be noticeable.