I think you answered your question. I like to keep things original sometimes (my '62 Dart is 98% original), but you're pushing a rope to make this 273 do what a 360/5.9 will do easily, and which will fit what you state you want. The 360/5.9 doing what you want won't take much work. The later Magnum's come with higher CR and better heads out of the box. Refer back to post #14.
