351C
66 and later 289/302, 351 W, and 351 Cleveland all use the same bellhousing, flywheels, and engine mounts, up through 84.
I never cared for the looks of the 65 Fairlanes, they looked just too boxy to me, but my Mom had a new 65 Comet Caliente, and that was a pretty sporty looking job.
Putting a 351C into one of those Fairlanes shouldnt be a hard task at all. As for the Fairlanes, I always liked the 64.
If you find one that has the origional drive train in it, and you want to use the origional transmission, you will have to change bell housing. On a side note, up through 64, Ford also made a 2 spd Fordomatic. Dont even bother with trying to hook that up behind your Cleveland, it wont hold the strain. The bell housing wont work.
You will also find a myriad of automatics back then as well. There were C-4's that came out in 64, C-6's that came out in 66, and the FMX series that came out in 58. The FMX series are easy to spot, as they have an aluminum bellhousing and tail shaft, with an iron casing. Those are a real rock crusher transmission, and will take a lot of abuse. They have a bolt on bell housing, and they were used behind just about every engine ford has made since 58, and in many configurations, so if you want to use one behind a different engine than it came out with, just go to your friendly salvage yard and get the appropriate bell housing. In my honest opinion, while they are somewhat heavier than a C-6, I prefer them as I think they will take more abuse. Some were even made with a rear pump so you could actually push start them.
I guess I should mention the C-5, which is a modified version of the C-4, and other than a little heavier duty unit, are for all intents and purposes, the same trans. Not sure what the differences are in them. On the C-4/ C-5, you will find there are two different types of bellhousings. One that bolts to the front pump and one that bolts to a flange on the casing. You can use either bellhousing with the later model, which has the flange, but you cant use the flange bellhousing on the older style that bolts to the front pump.
The Select Shift valve bodies came out in 66. Prior to that, when you put your trans in 2nd, it started in second but would shift to high on its own. All the 3 spd automatics were like that up through 65, then in 66 all went to the select shift.
One nice thing is that the valve bodies will retro-fit.
I forgot to mention, the C-6 is a unit cast housing. Tailshaft housing body, and bellhousing are all one piece.