From 1962 to 1964 1/2, Ford used the 170 cubic inch 6 cylinder engine. This was an inline straight 6. The 170 engine was discontinued in the summer of 1964. The 200 engine was used until 1978, at which time it was discontinued as well.
In 1965, Mustangs were outfitted with the 200 cubic inch 6 cylinder engine. At first glance, these engines look the same. There are some major differences, however. The main difference is a 170 engine block and crankshaft has four main bearing journals, while a 200 engine block and crankshaft has seven main bearing journals. Thus, the cranks and blocks are not interchangeable.
A noticeable difference between the two engines is the 170 engine has three soft freeze plugs on the right hand side (passenger side) of the block, while a 200 engine has five soft freeze plugs.
A subtle difference between the two engines is the timing cover. The 170 engine’s timing cover does not have a bolt hole in the bottom for an alternator or generator mounting bracket. The 200 engine’s timing cover has a bolt hole for mounting the alternator bracket.