Swapped engines and want to use factory tachometer

I have the truck listed above. I have done an 1995 Chevrolet 4.3 engine swap with hei distributor. I want to use the factory tachometer which worked off the coil, but when I hook the hei wire to existing tachometer wire tach doesn't work and my volt gauge goes crazy. I was wondering if a tachometer filter would fix this.