put your head on straight!

I recently assembled my 87 ford mustang 5.0 engine the last winter. when I built the engine with a few performance parts including gt-40 heads, trickflow cam, underdrive pulleys and a good msd ignition system. When I got the engine togeather and in the car I noticed that I somehow put the heads on backwordsdon't ask me how. the engine still seems to run fine without any complications, but I was wondering if I was missing any power because of the fact? the only things that seem to be bothering me about the car is that the engine is kinda hard to start when its cold, it also keeps running for a good 2-3 seconds after the key is turned to the off position, and there seems to be more smoke comming out of the passenger side tail pipe then the drivers side. I have tryed messing with the timing but it hasn't seemed to help any. keep in mind that this engine is carburated and is placed in a 96 mustang that used to have a 3.8 V6. if anyone could help my with this situation that would be great! im looking to pull then engine out this winter and do a few more upgrades.:SNSign: