Depends what your going to do with the machine, if it's VFR then what's wrong with what Mr X's said?
Old bombs like Pipers just had
Airspeed/Tacho then mag compass with Altimeter/combination gauge
the combination gauge was just oil pressure/oil temp
Really that's all you need, whack a garmin on the dash and your set to tour. Some want tripple IFR garmins with world data bases, just in case they do the round the world trip some day or two ILS's in case they happen into cloud and need to do an approach down to minimums into Mascot.
Some say you need an engine anylizer with five pickups' on each cylinder and gami washers on your needle and seat so yoo can lean it to within a mm of it's life.
So waddya want to have an all singing all dancing bells and whistles jobby or just go for a fly? Choice is yours.