First decided what kind of HP you want to aim for. Then decide if you want room to open up the intakes a little to add more HP/Torque in the future. Without free flowing heads you probably wont notice much but, if you are aiming for low end the Gt-40 and Cobra will work. If you are looking for a little more top end or intend on force inducting it go with a Trick Flow or Holley. Hope that helped.
For a stock motor, your best bet would be to stay with the GT40, explorer or cobra unit, or even send your lower out to get ported. But like pony girl said, depends on your combo and intended use
Well Brent, I have a 87 Gt and I just replaced my whole manifold setup, if and I mean IF you plan on making any other adjustment's such as head's, cam, a blower than a GT40 , Eldelbroch Rpm II, Victor or Performer wil be the way. If you plan on on leaving everything stock and you do not want to loose any Bottom End power[idle to 6500 rpm's] For the money you can get a Trickflow maniflold setup upper and lower for $399.99 http://www.brothersperformance.com/shop/mustang/tfs51500001.html
If you do not to just stay stock go with the GT40 or eventually the Victor5.0 by elderbroch just keep in mind that the Cobra manifold kit and GT40 DESIGN IS OLD damn good but a little old If you call around it may be hard to find a cobra because Ford is Redesigning their manifold's to keep up with the new one's I was going to go with the Cobra but that was the problem I ran into I call everybody including Ford......GT40 and the Victor are going to cost you about 650 to 750 dollar's no The TRICKFOW is designed specifically for the 5.0 and believe me it makes a big Damn difference I have pretty much all stock except Mnaifold system and Throttle Body Spacer etc. and I spent about over all 800 THat included though alot. Fuel Injector's Rebuild kit 2$ a pop you will need 8 Fuel Line removal tool 5 Buck's new manifold bolts' for the lower{you take 4 of your old ones and cut their head's off and use them for guide's when installing the new lower manifold.} BBK 65mm TB and spacer new Pvc valve and gromet REPLACE ALL OF YOUR PVC HOSES I DO NOT CARE HOW WELL YOU THINK THEY ARE, could cause a vacume leak later MAKE sure you by a torque wrench. and have patience because your going ot be doing some cleaning. Before you know it you'll be running in a raped ape. Oh yah, if you do have a high idle Make sure you bolt's in the back are good and snugged...........Many other guy's will disagree with my advice but for the money you can not go wrong......and yes you will notice a BIG DAMN DIFFERENCE. Good Luck on your desicion also if you want to go bigger when and if you get the Trickflow you can keep the lower manifold and replace it with the TRACK HEAT and other manifol'ds made BY TRICKFLOW go to there web sight and look at the spec's .....
gt40 flows great... expensive though. gt40 flows slightly better than the cobra... stay with those two for stock motor. the problem with the gt40 upper is that it's runners are allready maximized, so porting it would be impossible. gt40 lower intakes can be ported though, but not needed on stock applications with stock heads...
Grab a V8 Explorer intake. They are the same as the GT40/Cobra, and can be found for cheap. I got mine off of a 97 V8 Explorer, and painted it. It looks good, and it's gonna work awesome. Paid 150.00. See the link in my sig for pics (last page) .