the problem, with the oem gauges for your GA or aftermarket ones is you need to find a place for the sender, normally the holes in these have a sender it needs for the pcm. thats where the ease of obd2 comes in. with a 25 dollar obd2 to bluetooth adapter and a 5 dollar app(torque) i can see speed, tach,etc, and setup a gauge in the dash mode for any of it, trans temp, slip, knock retard for tuning, whatever you want. and you can use your phone or a cheap android tablet, have seen a bunch from 50 bucks this time of year.
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock