WHERE DID U PUT UR AFTERMARKET STEREO & SPEAKERS
Just remember when it comes to modern stereo anything being visible in a classic car.....it'll look completely out of date in 5-10 years.
My preference is to have everything hidden or at least only hack into things that are easily fixed. You'd be surprised at how good a cheap bluetooth amplifier and an underdash speaker can sound. Running speakers on the trunk divider in a fastback isn't the worst thing in the world either since you can easily cut a new piece of wood and set it back to original.
I'd roll with the under dash speaker and your kick panel speakers and see if you're happy with the sound before proceeding with putting speakers in the back.