I'll bet the big block tach-to-firewall harness is the same small block one....they just use a longer wire from that connector to the further-away coil on a big block.
I think you might find your B'Cuda has the tach wire going through the bulkhead connector, as B'Cuda's had the tach in the dash, not the console. I stand to be corrected when you get your car back!
