Smoking, idle problems 94 5.0 Help!!!

Alright I recently put in a 306 "built from a shop" well anyways Im having problems and before I tear into anything or take stuff apart I would like someone elses guess/fix Ok.. Well the car runs pretty good when it wants to.. I get a pulsating idle when I first start the car up in the morning.. but when I drive for around 2-5 min it stops pulsating.. but it will sit at around .800 an will be hesistate every few seconds.. An well.. When I get on it like 3rd/4th/5th "Catching up with high-way traffic Im noticing alot of smoke coming out of the exaust.. Whitish smoke but doesnt smell like burning oil.. I check my oil after every drive and it stays around the same. At certain points when I take off it seems that my cat's are plugged they have a muffled sound coming out of them. It doesnt smoke all the time only when I give it -WOT- an it stops when I left off the gas/ I thought in the beginning maybe one of the piston rings didnt seat right.. SO I used lucas on it and it didnt really help at all.. Also when I come to a complete stop and turn the car off smoke comes from around the headers, and also from the front of the car for around 1-3min If someone has had this problem or knows what to check it would be great! If you would like more info on someone I listed I will be sure to let you know!!

Thanks

P.S Im just nervous I dont want this car to blow up.. It ran good for a 2k mile drive from Michigan to Arizone only thing it would do is smoke!! I also have to replace the valve cover gaskets they seem to be leaking.. Changed valve covers and the gaskets looked good still but yea shoulda replaced them!

coolant?? how would that come out from the exaust?? or how would I fix it lol Ive never had cars smoke before so its the first for me.. yea imma fix the valve cover gaskets asap but still tryin to figure out the smoking part... I mean it smells really funny too like burnt fluid but I dont see how it would be coming out of the exaust thou

the oil is great! no milky rez or anything.. Yea it seems to smell like coolant but the levels are fine at one point the big hose had a hole so possibly it is still burning it off the motor area..I know the valve covers have to be replaced they are leaking bad so I have new ones to put on there I also have to replace the hose's underneath the upper plent."Vac lines" they are leaking they were not in the best shape.. The heads are recently rebuilt too.. I just cant seem to figure it out but remember from my first post.. the cats seem to be plugged up because my buddy was looking out the back of my exaust " No mufflers" and it was spittin stuff out too and it really really smokes when you turn the car off and just noticed its coming from inside the cats

hopefully there are still some other peeps out there that can help

Thanks!!

its a 5-speed so that vac line is out of the question.. Yea Imma go through everything 1by1 when I actually have a day off haha.. Yea imma clean all the sensors and throttle-body I mean today actually I seen no smoke coming from the front of the car until I shut it off and 30 sec later it poured from the front grill area so imma check to see why.. and it stinks to high hell but other then that it needs a hella tune-up cuz im sure my air/fuel timing is off so.. I'll let the shop do all that!

Someone mentioned earlier that could be a coolant leak .. combustion problem.. instating.. bad lower intake gaskets or possibly head gaskets?? Also it was mentioned I would see milky white in my oil.. but its still normal.. Im totally lost so I will be posting videos of what it is doing! SO that should make it all a bit easier for everyone!