Without the correct gearing, you will not get the benefit of all that advertised HP. If the engine is forced to lug around at low RPM, you will be worse off than with a stock engine. It will feel very sluggish and fuel economy will be terrible. ATK also recommends a higher stall converter than stock. If you don't want to change the gears and converter, you would be better off with a milder engine.

Depending on your tire size, you might get by with the 3.23's. The cams in both engines are for building power and torque in the midrange to high RPM's. The cam I had in my 383 was milder than the one in the ATK and I barely got by with 3.23's. The 383 is good at making torque, but the cam still programs the power characteristics of the engine.

Sorry if this sets you back, but you need all the info before spending all your hard earned cash.