Thanks for all the insights guys.
The last owner of my 66 b-cuda cut into the doors to add fronts and the rear divider to add rears.
With my interior almost done and the cost of interior door panels I'm not about to cut into them so I'm going for the kick panel option and under dash combo up front. However I'm still wondering about a low impact option for rear speakers and a fairly OEM look. My best thought is the rear divider that I rear made, but not cutting into the carpet and instead trying to hide them underneath, not sure on sound though.
I don't mind adding a sub under a seat or in the spare tire (trunk). But again where to add the rear speakers.... I'm currently going to go without and see how it sounds with the dynamat, new interior and new system. Always open to thoughts.