possible rebuild and performance mod

ok guys;;;thinking going rebuild my 1986 industrial cummins 5.9l 12valve engine;;going be making some long pulls this race sason and few weeks back while driving truck I was getting major white smoke out of exhaust;;bad enough when I pulled up to stop sign couldn't see out rear window due to white smoke;;only did it for that day;;;a couple weeks later I was letting truck idle and notice excessive amout of white smoke coming out of blow by tube;;and drove about six blocks and eng was running close to hot mark on temp gauge;;had a guy say was just a injector maybe hanging open them 2 times;;i'm thinking maybe I should rering and rebearing it and put new head on it[found new cummins heads on e-bay for $600.00]just thinking since be doing some long hauls this season I don't need loosing engine 1000 miles away from home;;
since thinking rebuilding thinking should also replace injectors[never had anything done to them]while i'm down what should I do to gain performance and mpg dueing eng rebuild?what things should I replace and what should I replace with;;maybe a parts list of all right stuff to do to make a good reliable and more performance and mpg;