Electric gauge, smith instruments vs MSD 5520

I might have a problem on hand here, i asked smith how to drive their GT40 spec tacho gauge, and the answer seems to be that MSD 5520 make to large of a signal voltage and it just swamps the gauge and it drops down to zero instead.
Since this seems to be a theoretical problem so far (since i haven't installed it yet) I am asking if anyone out there has run a MSD 5520 with gauges from Smith instruments for their GT40 build, and what was the result of that?
For knowledge i plan on running Holley terminator X MPFI with MSD 5520, and was planning on running the tacho gauge from the out signal from MSD 5520 module.
Do i need to change the plan and use a PWM output från the engine management system instead, or is there a solution to get it working from the MSD 5520?

Posting image from Smith instruments manual for the gauge. (Maybe i should take the signal from the coil instead?)