Any alternator provides the ability for a simple revcounter installation
. A wire can be soldered to the AC supply before the rectifier and this is the feed for the signal. Any automotive electrician can do this for you easily. VDO (and many other brands) provide off the shelf gauges for this type of installation
and they can all be calibrated for different pulley sizes. The electrician will be able to calibrate it for you with a photo
tach but make sure they do this at you normal operating revs as there is often a bit of inaccuracy at low revs. While you've got the alternator off, take advantage of the work & get it serviced.