I don't own a '64 Fairlane with a FE, but I've looked at a couple real Thunderbolts, and a bunch of clones & racecars - I agree with Doug, adjusting valves shouldn't be difficult. I included a good picture of John Calvert's '64 Fairlane Stock Eliminator drag car, you can see it's a pretty open shot to get to the valves, relatively speaking. I also agree with Doug, all my hopped up FE's have been solid lifter, rarely do the valves need an actual adjustment past the initial break in time when I check them, so it's not something that should need constant attention.
I believe there are basically a couple FE to C4 adapter bellhousings - the one JPT ( Jim Paquet Transmission ) used to make, and the one PA ( Performance Automatic ) makes. The PA one is SFI certified and I think thicker aluminum, but I don't know if there are any issues to the trans tunnel. There may be a difference too in the type of C4 each adapter uses, I think the JPT needs a pan fill type C4 case and the PA can use a case fill type C4, maybe someone here can verify that. '64 Fairlanes did come with a C4 though, so I think as long as the transmission location stays close to the same it shouldn't be too bad, but just a guess. I think people also make their own FE to C4 adapters out of aluminum FE FMX bellhousings.
Again, no personal experience setting up a '64 Fairlane with a FE, but cars that are primarily used for drag racing often use the OEM front springs from a small block or even 6 cyl. combination, they may or may not work well in a car that is primarily street driven, but worth trying. A local spring shop, or a national shop like Eaton spring can help you select proper springs too, and make you springs if needed. Some of the answer will depend too on your particular car ( how much it's been lightened ) and the FE you use. FE's can be relatively light with aluminum heads, aluminum intake, aluminum bellhousing, aluminum water pump, and so on.
