the 410 comp cam is what you want for a sronger torque curve. Remember Delta-cam rockers are well suited for the upgrade, you will need 5.525" pushrods for the delta cam rocker arms and the comp cam. You will need 5.550" length pushrods if you use the stock or equivilent rocker arms. That is of course, you dont deck your heads or do very minimal decking (.0001, ten-thousands of an inch wont effect it)
Porting the 4.0 heads and lower intake will help tremendously with both torque and hp. You probably will be happy atleast porting the lower intake. I feel the 4.0 isnt lacking too much in the power department, than more so a broad RPM range. The cam will help that. The 410 cam redlines at 4800, compared to 4200 stock. 422 cam redlines at 5200. Both the 410 and the 422 use the same length pushrods, but the 422 requires dual valve springs. Although, it wouldnt hurt to use dual valve springs with the 410 cam.
good luck. You can always up the compression to gain a substantial amount of power