The AutoMeter seems rather pricey. By the time you've bought it, and a suitable tach, it looks like you'll be close to $200. And you'll have to modify your alternator.
A better choice might be to replace the alternator with one that has a tach output. As an example only, I found one on Amazon for just under $80 (not sure if this exact one is a fit for you, but you get the idea.) Then you could install a standard diesel tach, which can be had for as little as $30.
https://www.amazon.com/New-Mercruise.../dp/B00E9G07JK
https://www.amazon.com/MOTOR-METER-R...e%2C148&sr=1-6