What the HECK major backfire now!! Any ideas??

So you did take your plugs wires off? That is what it sounds like to me, and if you are positive that you have the wires on right then loosen the distributor and keep turing it back and forth wile trying to start it. It should run good enough to get the timing set.

dizzy

your dizzy might just be bad? they go bad on the random sometimes

Not 100% sure, but whenever I've had LOUD backfires (not the little ones from running rich) it's almost always been a problem with either the distributor or the plug wires. Keep checking those, I guess, it sounds like some wires may be crossed...there's also a diagram somewhere in here that shows the hookups for the Cobra intake, but I don't know who posted it, you could probably find it in a search. Good luck.

make sure if you have an H.O. motor you use that firing order. The Non-H.O. motors have different firing orders

5.0 H.O firing order 1-3-7-2-6-5-4-8.

Here's some distributor install tips...

Take the coil wire out of the distributor. Pull #1 plug, put your finger in the spark plug hole. Have someone crank the engine until it starts to blow air past your finger. Stop cranking, turn the engine by hand (breaker bar on the harmonic balancer bolt, or put the car in gear and push) until the TDC mark on the harmonic balancer lines up with the pointer on the passenger side of the engine. Loose the distributor hold down bolt, remove the clamp, cap and wires, disconnect the wiring harness. Pull the distributor straight up.

The following re-install depends on the engine being lined up as in the previous instructions.
To re-install, turn the distributor rotor to point to #1 cylinder position on the cap. The#1 position is about 11 o'clock if 6 o' clock is the front of the engine. Line the rotor up with it pointing at the #1 spark plug position on the cap and drop it in: you may have to twist the shaft some to get it to engage the oil pump shaft. Then remove the SPOUT connector plug, and use a timing light to set the timing. The SPOUT is the dangling connector on the distributor harness on stangs made prior to 94 and with a computer controlled engine. 10* is stock for most 5.0s' 12*-14* is good for more pep if you are not into NO2 or power adders.