Surging & misfiring in a semi rebuilt ford engine.?

Perhaps rebuilt would be the wrong term here, more like freshened. My 84 Ford Bronco has a 351 HO Windsor engine that ran as smooth as a kitten, but leaked oil everywhere & had a bit of water coming out of the exhaust. So, I tore down the engine to nothing but the block, leaving the crank, pistons & cam as were. Turns out the engine had been bored 40 over, a performance cam, lifters & push rods, but that's beside the point. I replaced all the gaskets from the oil pan up, new oil pump, timing chain & gears, sanded down the buildup off the valves & replaced valve seals. Same carb, but new plugs, wires & rotor on. Distributor never moved. It now runs, but has a miss I can't place to save my life. I've checked around the intake, vacuums & plug wires. The timing gears lined up perfectly so I'm at a loss. When you watch the tach, the needle surges like crazy, both in park & under load. It's not an outright backfire, but it does sound like there is some amount of detonation occurring outside the chamber, in the manifolds. If you hold your hand up the the exhaust, some hits are harder than others & when we took it out on the road, after it's warm, when you come to a stop it dies. Can't understand what i'm missing here, so maybe an outside opinion will help.