a .060" overbore would definatly help unshroud both valves. going down to a 1.88 on the intake would help a bit, but the 1.62 exhaust is still really shrouded. I am in the process of a similar build. one major help is to lighten up the internals as much as possible. chyrsler re-used the same forged crank as the poly 318, so in order to get the smaller 273 pistons to ballance they used a wrist pin which weighs 320 grams!! Keith black has the correct length wrist pins which only weigh 107 grams. then you just have the crank ballanced, preferably by taking weight out. I have a cast crank too that i am using, but i havn't gotten around to weighing the difference.
With the notching of the block and using the stock magnum valves, the max lift you could safely run is .525", which is the max for these heads anyway. But for mileage, a big cam is not wanted obviously, but a good comp extreame cam, like the 262, would be a good 'performance' choice, and still relatively efficient.
JJ