[66fastback]

The 88 heads (E7's) will bolt right on, BUT you will definitely lose compression (and power and mileage) making that swap straight up on a 289.

You don't NEED a roller cam to run those heads, or any head with "roller rockers", but you would probably need to check the push rod length once installed. It is possible that you would need a different length. The push rods from the 5.0 WILL NOT WORK in the 289. The 5.0 roller blocks have taller lifter bores for the roller lifters, and therefore shorter push rods.

The Headers on the 5.0 will not fit on the 67 either. The late model cars don't have the shock towers in the way like the old cars, so they have a lot more room to bend the tubes, and they take advantage of that room. I know, I have a nice set of Mac headers that came on the 5.0 that will not fit on my car.

How do you know you have a dead cylinder? I know you said you have a "miss". Have you ran a compression test yet? The pistons and rings on those 289's are usually pretty good (nice long rod to stroke ratio), but like you said, the valves are a different deal. I almost always had trouble with leaking guides and/or worn seats.

I'd start by checking for good spark at all the plugs, and if that checks out, do a compression test. If it's just heads, its your call as to whether you just rebuild the 289 heads or if you swap out the engine for the 5.0.