You have several choices.
Your FLAPS has any number of el-cheapo (and a couple that aren't) tachs that will work with your engine (just make sure that you buy one with the proper number of lobes), but they usually don't look very pretty.
The aftermarket gauge companies sell them, and they usually look pretty nice, but they're expensive.
You might try looking on ebay for an old sun gauge and sending unit. Those were used back in the day. For a 6 cylinder engine, you'd want an EB-7(a) transmitter, and for an 8 cylinder engine, you'd wan an EB-9(a). Any of the old-school black-faced gauges would look right at home in your cab. They used to make mounting cups that would clamp onto your steering column, so no cab modification is strictly necessary.
Some of the gauges go for a pretty penny, though. FYI.
