gt40x heads on 94 snake???

Unless the gt40x runs a 2.02 intake valve then no; you can use any of the basic cams usually under the .520 lift using a standard 1.6 rocker without issue. However if you plan to use the stock cobra 1.72s (if those heads are pedestal mount) you might want to look into a slightly smaller cam and using the extra rocker to make up for things without getting into piston to valve clearance issues. At worst you can always clay the heads when you put them on and see what your PTV clearances are.

If those heads use a 1.96 intake valve you are cool if, they use a bigger then yes you will need to flycut. I thought those were just the aluminum GT40s; he might be thinking of the new z casting gt40 which would require a cut.

Here is the copy/paste from summit:

Highlighted are the parts you should be concerned with.

Brand Ford Racing
Manufacturer's Part Number M-6049-X307
Part Type Cylinder Heads
Product Line Ford Racing GT-40 Cylinder Heads
Summit Racing Part Number FMS-M-6049-X307

Cylinder Head Style Assembled
Cylinder Head Material Aluminum
Cylinder Head Finish Natural
Combustion Chamber Volume (cc) 58
CNC-Machined Combustion Chamber No
Intake Runner Volume (cc) 178cc
Exhaust Runner Volume (cc) 62cc
CNC-Machined Intake Runner No
CNC-Machined Exhaust Runner No
Intake Port Location Standard
Exhaust Port Shape Square
Exhaust Port Location Standard
Intake Valves Included Yes
Intake Valve Diameter (in) 1.940 in.
Exhaust Valves Included Yes
Exhaust Valve Diameter (in) 1.540 in.
Valve Springs Included Yes
Outside Diameter of Outer Spring (in) 1.500 in.
Damper Spring Included No
Number of Springs Per Valve Single
Retainers Included Yes
Retainer Material Steel
Locks Included Yes
Lock Style 7 degree
Valve Stem Seals Included Yes
Valve Stem Seal Style Umbrella
Rocker Arm Studs Included No
Rocker Arms Included No
Rocker Arm Nuts Included No
Guideplates Included No
Guideplate Pushrod Size 5/16 in.
Accessory Bolt Holes Drilled Yes
Valve Guides Included Yes
Valve Guide Material Bronze
Valve Seats Machined Yes
Valve Seat Machine Style 3-angle
Valve Seat Material Steel
Steam Holes Drilled No
Oiling Style Through pushrod
Machined for O-Ring No
Heat Crossover No
Quantity Sold individually.
Notes Designed for bolt-on rocker arms.

You should be just fine running those heads without cutting the pistons. It is suggested to run hardened pushrods with guideplates. The ford racing ones that are the normal stock length are only like $40 and are hardened. I'm not sure if the cobra runs a different length. The bolt on rocker is the pedestal mount; so you should be fine there aswell. Although a custom cam is likely the best choice; you can run an off the shelf cam just fine. I enjoy my trick flow stage 1 which is .499/.510 221/223 @ 112lsa. The ford racing cams are all 'box' so the lift split is the same on intake and exhaust...they work but there are better choices. Be sure not to go too big though as you will need to compensate for that rocker. For instance that stage 1 cam would be a .512/.522 with a 1.72 rocker putting you around the max safe lift on the exhaust side with a stock piston. Just some food for thought.