different tach's???

[BUXMAN66]

i bought a tach dash off of e-bay (board member),and after doing some talking w/ the guy's at restoration world (full line of gm cars and trucks restoration parts)...and then his supplier.....american autowire......i now have been told that there might be a possibility that even w/ the correct style harness to hook up w/ my hei ignition...that gm had different styles of tach's and that some were only compatible w/ points/coil style of ignition. can anyone shed some light on the subject.....and also what the hell am i gonna do w/ a coil type tach...and i've got the hei style ignition?? any way of knowing/identifying this beforehand or is it just hook it up and hope??