Balancing an engine mostly involves weighing the piston/rod assembly and making sure that all four assemblys are within a certain tolerrance of each other. The heavier rods and pistons have a very slight amount of material removed from them to equal the lighter ones. To have the crank balanced involves spinning the crank (most of the time with the flywheel clutch installed due to its heavy weight) and removing material from the crank in heavy spots and that would give you a completely balanced engine. So anyway what Im saying is that its a lot easier to get the engine balanced when its not put together yet. Im currently having mine balanced at Dwans in pinellas park. The cost balancing the pistons rods is $100. As for the head porting and polishing it might be a better idea to look for a new performance head with stainless valves even though expensive might be a better overall deal. After spend anywhere from 300 to 500 for a port and polish then new valves cleaning it new seals and seats you could pay more than a new head. Also the more valve jobs done on a head the worse it becomes.