Go to your nearest AutoZone, or eqivalent, and you can get a tach that will handle 4, 6, or 8 cyl for under $50. How soon do you need it? I have one that I bought for the Corvette when the OEM one was dead but found there was nowhere to mount the damned thing. I'll let it go for $40.00. It's new, in the box.
Jim