non-DFI tach question

[brucep at ptd.net]

I've searched high and low and haven't been able to find any info that was
of any use on this subject so I am turning to the "minds" of this group.

I am building a steady state dyno and need to add a tach to it. I want to
measure the shaft speed of the dyno. (I don't want to read the engine
ignition) I can't afford a digital tach setup so I am looking to use a
analog 4 cylinder tach I have laying around till I can afford to upgrade.
What would be the easiest way to make this work? Does the tach sense the
drop of the ground when the points open. Could I use parts from a GM 4
cylinder HEI coil ie: coil pickup and ignition module. I think I am headed
in the right direction just need some advice on different ways I could do
this. Ideally I would like to have a digital display which would allow me to
have a more realistic reading of rpm's as opposed to well it looks like it
is 2000 not 2010, 2020 or 2050. Any help would be greatly appreciated. And
sorry for taking up bandwidth for the non-dfi post but this was my last
place to ask . . . thanks in advance.

Bruce