Rick - Every HEI module has a warning that they will damage old style analogue tachometers or at least, notes that they do not support them and almost all manufactures offer pre-made filters for old analogue tachometers. Some have to be matched to the ignition module others are more generic.
That said and your admittance that electrical is not your strong suit maybe making your own adapter is not the right solution.DIY Tachometer Filter
Jim's instruction list for the parts required including the 270 ohm, 1/2 watt resister. https://www.radioshack.com/products/...-resistor-pk-5
is bare bones but so is the filter he came up with. It is a simple easy to make and no frills. You can send him a message if you have difficulty or contact him at his site Camaro forum FirstGens.com
Having us post a warning here at Team Camaro is a bit like locking the barn door after the horses have run away.
All the reproduction first generation tachometers including OER for Camaro's I have seen are all marked not for HEI systems, and most catalogues and websites that sell them also state they are not for use with HEI systems. But all is not lost if you already have it installed on a HEI system. For others reviewing this thread with a new in the box OER and or STILL working but flaky, jumpy, or incorrect original tachometer and new HEI system, unplug the tachometer NOW and take a look at purchasing one of these smart modules. This TachMatch module sounds like a universal translator:
TechnoVersions - Home of TachMatch, MeterMatch and MotorMatch
Useful for those folks who have just done an engine swap.
But is sounds like the best solution for you Rick is to just buy a replacement circuit board for your blown OER tachometer:
Greg sells this one: Team Camaro Classifieds - All Years - 69-77 tachometer circuit board - NEW!
And can customize it for you.
Or Randy C's Tachometer shop can replace the circuit board in your tach with a newer style board that will work correctly. Services - RC Tach Shop
You can reach him at (812) 989.4727 (812) 284.2555. Randy - firstname.lastname@example.org
Either of these guys can get you a working HEI style replacement board for the OER tachometer and it sounds like the cheapest solution as it will revive the tachometer you have already killed so you save the replacement costs.