Any 302 and 351 heads fit and some 289 heads are desirable. The reason that I say some is the fact that some very early 289 heads have small valves. There is variation in combustion chamber size and some of the early 351 heads have larger valves similar to the GT40s. Early heads use the large spark plugs and there are 3 different rocker arm designs that evolved through the years. Stud mount, stud mount rail, and pedistal mount. Any of these designs can be used on a 302 as long as the correct rockers and related parts are used.
The early 351 heads will have coolant ports with a "Dog Leg" shape which will require intake manifold gaskets that are made to seal the port to a standard intake manifold.
There are some California smog heads that have external thermactor air inlets, next to the exhaust ports, that you will want to avoid, but they are rather scarce. Later heads will have larger combustion chambers and the GT40s are no exception. With standard pistons you'll get about a 9:1 compression ratio with the GT-40s. Cast iron holds heat more than aluminum, so an iron head with a 9 to 1 ratio will have the same effect as about 9.5 to 1 in aluminum.
On some later heads the exhaust ports will have internal thermactor porting and a restrictive "Hump" in the exhaust ports. The humps can be ground off. The inlet of these ports is in the back side of the heads (GT-40s, too, but not GT40Ps). They will need to be plugged with straight thread set screws or Ford's special plugs. The size is 5/8"-11 X1". If they aren't plugged, you'll have an exhaust leak facing the firewall. The GT 40P has relocated spark plugs and no thermactor ports. The plug relocation will cause clearance problems with some headers and exhaust manifolds.
You mention that your engine is a mid eighties engine. The 1986 only 302 (5.0 HO) engines have pistons that are true flat tops that don't have valve reliefs. You will need to change out these pistons or else you will run into valve clearance problems. Their 86 only heads (The engineering number cast into them will start with E6) were junk. Avoid them, they are not good for performance use. The combustion chamber design shrouds the valves.
You don't mention if your engine has a roller cam, but Comp Cams has a series of cams called 'Thumper" that are designed to have the lope that you like, but still retain drivability. I think that they are available for flat or roller tappets.
I recommed that you get a copy of "High Performance Ford Engine Parts Interchange" by George Reid, SA Design P/N SA56 | 
