Hi Vanagonners!
Got a bit carried away due to the fact that it´s FRIDAY, will try and get it a bit more serious!
Q about Gauges
Well I would go for three add. gauges.
Revcounter, voltmeter and oil pressure or temp.
In europe anyway, you buy 52mm (ab.2") or 70mm(3") gauges.
I don´t know how your Vanagons are built, myself I have a standard -88 (Transporter) and I see three obvious places for them: the revcounter in a mount on foot between the instrument housing and the ashtray ( big flat metal surface) and the other two -a pair of 2"- in the likewise flat metalsurface to the right of the radio, above the glovecompartment in front of the passenger . The last place being insted of the plastic cover in front of the gearstick, there is room for a mounting box there.
How could I be so stupid as to put it in front of the passenger?
Well, I would buy mounts for the gauges so that they ar connected parrallell to the original warning lights!
Then I get the light signal in my face and could take a look at the gauges to see what´s wrong.
It´ll also give my passenger something to do during those long midnight drives and hopefully keep his/here fingers off the Stereo!
Why a volt instead of an ammeter?
Don´t know!
I think it´s more interesting to know how much power i have in the battery than how much the alternator is pumping out, and it could be nice to know how much there is left when  you´re parked too ( I hook it up to the lightswich so I will be able to just put the parkinglight on and read it at night)
Wheather you use oil temp or pressure is up to you AND the conditions in wich you drive, up north the pressure is more interesting while you under warm conditions are more interested to know if the oil is transforming into " water" due to heat buildup!
BTW, that place where I suggested you put the revcounter I use for my cellphone mounting ; advice and doing isn´t always the same!
Good luck!
Calle -88 Vanagon, Saab 99, 4 dogs etc.
Mullhyttan Sweden.