Thanks, agree the Holley cover might be the best option. Was really hoping to convert/use the HEI tach signal as I only need trans control and no EFI/Ignition
I have used the Howell EFI swap which uses a modified tach signal. The system seemed more reliable after being changed to use a proper square wave signal generated by a GM ignition module.

HEI distributors with 4 pin HEI module can be converted to 7 pin HEI module. 7 pin HEI module supplies a REFerence signal just like the one the 7427 is designed to work with.

http://www.useasydocs.com/details/GM_7pinHEI.htm
https://macswebs.com/qdtech/tech/hei.htm
https://www.binderplanet.com/forums/...ersion.128469/

Note that you do not need to secure the weights or vacuum advance because you are not using the computer to control timing.