My first car was a 66 Mustang straight six, 200 cubic inch. I loved it. I did some mods and dialed in the suspension with Koni shocks, the Shelby mod on the upper control arms, larger sway bars (front and rear) and stiffer springs.
I then installed a Weber progressive 2bbl carb on the log intake manifold. I milled off the single carb mount and brazed on a steel plate. It worked perfectly, once the jetting was sorted out. I had the car down to 7 seconds 0-60. Not bad for a straight six. Plus the Weber carb increased MPG quite a bit. I milled the head 060 thousandths to increase compression.
While a Mustang could not compete with a modern car, they can be made to drive quite well. Mine was certainly pleasant to own and very responsive, mostly due to the mods. In fact, in many ways, modern cars don't match it. About the only car that was more responsive was my turbo Miata.