Decent Slant 6 carb, intake, header setup

My mechanic friend suggested that I take the slant 6 out and replace it with a 318 with 360 heads. To do or not to do, is the question.
I love my slant truck, used to commute around town and run truck errands. But I fear the freeway. I only know Magnum 5.2/5.9... the blocks are nearly identical. I can't see a reason for the 318 if you have an open choice, with the 360 having so much more power under the curve in stock form. The numbers don't really reflect the difference you feel.