67 Barracuda with 383 and ECU… alternative engine harness options?

See in the parrts book if the same p/n is used for the LA engine and whether the harness with tach option is different.
Then once you knowwhat was made, try a wanted ad.
This way when people ask if you can use a /6 or LA engine harness you'll know the answer.

As far as ECU wiring - that you'll have to add yourself.

As far as venders for new.
Year One sells M&H
Bill and Rose Evans make and sell their own.

I think that's about it.