I don't know everything about this, BUT here is some of what I do know. The 1963-65 engines all have the bosses cast in the sides of the block for side motor mounts. That means you must have a 63 to 65 engine in a 63-65 Rambler. The American is the oddity here, it will take all 196s ( OK 1960 to 65 that I know) , as long as you have the right crank shaft in it. The early 196s used the two mounts off the front of the engine. They were bolted to a block plate that can be used on any 196 ( bolts on, not part of the casting) . The 63 used side mounted motors mounts and have bosses and holes for them, the 63 American had them too, just they were not used, and the front motor mounts were retained. In 63 ALL the 196 crank shafts had a "flat" mounting flange on the crank ( like later 290-343-390s etc with BW autos). Before this only the auto cars had this, the standard shift cars used a "volcano" flanged crank. This crank had for lack of better words, a volcano at the end of the crank. It is large, and you cant bolt anything to it. Then there are different size cam support journals. If you get a block, GET the CAM with it. There are no new cams, and you need the correct core that fits the block to have reground. Andre " A.J." Jacobs, web page http://southtexasamc.tripod.com (830)-980-3165 , akjamc@xxxxxxxx Owner & Proprietor, South Texas AMC