I would run the smaller one, TQ and mpg will be up, if you want a tad more get some 1.7 rockers to help out in the lift department without increasing duration.

A new magnum engine trick I just thought of... I just did a plenum gasket on a truck and added another spare plenum plate I had spaced about 1/4 inch down from the stock one and it seems to be running about 20 degrees cooler IAT by keeping the hot oil off the bottom of the intake. Pinging is pretty much gone also but some of that could just be not sucking in oil.

Not really much support for that computer but you can advance the ign timing by slotting the crank sensor mounts and get 2-3 degrees advance. I would try running a set of 460 ferd injectors to get a little more flow and better atomization. The fuel pressure on the earlier truck like that is a little lower than the later ones or I would recomend the 5.4 injectors.