I have a stupid mk1 with a clock in the dash, so number three is a VDO tach for me.
For early Rabbits, find an Mark I Scirocco dash cluster. With the directions for modding given out by some here you can even use the tach on your diesel engine. As mentioned earlier in this thread, a second (matched) sender into the lube system & a switch will get you oil temp readings on the stock water temp gauge. The 'rocco layout sure improved the appearance of our 1977 diesel Rabbit "Bronze Edition"(VW's code name for their
most cheaply-equipped version! The front door vent windows didn't even open!).
Personal preference... the stereo head unit can be moved down to the console, leaving more 'driver's-line-of-sight' space in upper dash location for the important gauges. Makes it easy to observe operating status without taking eyes off the road.
For the later Mk I and Mk II Rabbit/Golf/Jetta vehicles, AFAIK the Econo/Shift light mess can be pulled out (of a Mark II cluster), and a second temp gauge (or fuel gauge?) installed (as most Mk I instrument clusters
do have a gauge in that position, rather than the Achtung! light). OTOH it may be possible to trim away most of the case on an aftermarket VDO oil pressure gauge & fit that in there. Will be attempting that mod when adapting in a Quantum TD cluster (w. factory tach, similar to some G/J Mk II TDs) as part of upgrading an '80 VW Dasher TD's cockpit.
Counting on that to leave room for EGT, turbo boost & intake restriction gauges in former stereo head location. Digital voltmeter & WVO tank temp gauge make sense & are slim enough to fit in almost anywhere. Depending on what temps you drive in, an inside/outside thermometer is useful to predict road icing, but again, is available as a slim digital readout & easy to find a 'home' for mounting.
J.R.
SoCal