Mild Torque 318 suggestions wide open!

My son's 73 Dart is what you are looking for. Stock untouched 1973 318, Mopar Performance small hydraulic cam, Cloyes double roller timing chain, 1967 273 Commando intake and AFB. 1973 340 exhaust manifolds, 2 in duals and turbo mufflers all the way back, 727 automatic with 340 torque converter, 7 1/4 Sure Grip 2.76 gears, 15 x 6.5 original Rallye's with Michelin tires. On a trip it gets a little over 20 mpg with regular gas and cruises all day at 75 mph. Any cam from 260 duration to a stock 340 cam will work nice. 318 marine engines were rated around 225 hp with small heads and valves, and cam. The other alternative would be to buy new pistons, use 340/360 heads and intake, and basically build a 340. Should be over 300 hp easy.