I bought the 12 circuit harness from Speedway but have yet to install it. My Savoy is probably like your Barracuda with very few options so I think a 12 circuit would do OK for your car as well. I like the layout of the kit except for the GM based wire colors and column wiring is based on a GM style plug. The directions look pretty good but the fuse box will need to have a bracket made for mounting. I might get ambitious this winter and do the big job and fit my new headlight relay setup too with some new halogen bulbs.
The decision would be just rip it all out and start from scorched earth or replace it as I remove the old stuff

Gus