MustangForums.com - Need a little assistance please

So i bought a 99 GT from a tow yard and did a quick tune up on it, changed the plugs, a few COP's, the oil and filter and cleaner the air filter. I also changed the motor mounts and replaced the battery on it. I got it to start but noticed some white smoke coming from the exhaust. The car has a flat tire and the reg is expired so I cannot drive it at this time but let it run for a while and the smoke did not seem to go away at all. There was recent head work done on the DS because the head is spotless but the PS does not seem to have been removed. My initial thought was a blown head gasket but I ran a block test yesterday and the results came back negative. I cannot see any oil in the coolant and no coolant in the oil (milky color) and when I initially drained the oil, it was not milky either. I dont see any build up on the oil cap either. The intake seems to be a PI intake as it has metal near the front portion of the upper intake.
My question is, what are the chances of this being a leaking intake gasket (those seem to be notorious for leaking from what i have read?) as opposed to a head gasket? Also, if the head gasket was just recently done, could coolant just be burning from inside the cats? The car seems to have the stock H pipe with cats so I am sure if it did previously blow a head gasket, maybe it dumped a lot of coolant into the exhaust and since the cats werent changed, thats where the white smoke is coming from 9too optimistic? lol) The car sat for at least 60 days in the tow yard and did not seem to smoke when I started it there. I plan on doing a compression check this weekend as well to get some more clarification. Thanks for the help!

Edit: I am unfamiliar with the 96-04 4.6 engines so I am trying to do as much research as possible and am sorry if I am asking redundant questions.