I can think of no reason why you would need to change the bellhousing. However, during the thread I've lost track of the year of your car, if it is an early one with the extended crank flange your trans won't bolt up anyway to the late model motor unless you fabricate some sort of extension or adaptor for the crank. You'll need the oil pan and pickup from the 413 as the sump is further forward on the 400. You'll need to either change the water pump housing and all front accessories to the 413 stuff, or you can keep the 400 stuff, have your radiator modified or replaced (the lower spigot will be in the wrong place), and have a power steering adaptor hose made. If you decide to change to the four barrel carb, you can still get adaptors to use your 2 barrel manifold, or this would be an opportunity to put an aluminum intake like a Performer on for weight savings. -- Bill Parker, South Central Indiana '62 Plymouth Max Wedge; '64 Dart Convertible (Kathi's car); '65 Imperial; '65 Barracuda \6 (Kathi's other car);'68 Barracuda Fastback 340-S; '69 Barracuda Fastback now 360 (20 y.o. son's car); '72 Cuda 340