Heads, cam and intake are all part of the equation. If you are just looking for a cruiser, and not out for an 11 second E.T., there are several options available. For the money, "kits" like Edelbrock's top end kits are tough to beat. For the money, IMHO, about any aftermarket head will be better/less expensive than a stock rebuild, plus machine work. Keep in mind that with a new camshaft, you will change the power band that the car uses, and if you get too much lift and duration, you will need a new rear end ring and pinion to take advantage of all your motor work.
And then there is safety too. Are you working with 4 drum manual brakes? Or have you got a power disc/drum set up?
Of course, you can't expect the 40 year old transmission to put up with a new 500 HP engine, and so will need to planfor that.......It gets expensive pretty quick.
Have you got a good tune up on the car? Plugs, points, timing, carb cleaned out? If the timing gear set is original, that should be one of the first things you replace. It will cure a mulitude of driveability issues.
A quick check on summit shows these "C" heads..
http://www.summitracing.com/search/...351/Engine-Family/Ford-Cleveland/?Ns=Rank|Asc
If you are thinking about a cam swap, now is the time. Keep in mind that valve springs and camshafts need to "match" each other..If you stay at or under .500 lift, you SHOULD be able to not have to change ring and pinion gears. But do more homework. Each cam will have a "cam card" that tells you the minimum gears, torque converter stall speed, etc...