1985 chevy....need help...

Ok im 16 years old and i have a 1985 chevy 1500 (350)...i live in texas and im havin trouble passing the dang emissions test...the co2 or what ever is off by like 4 points...i mean what should i do? im thinking about savin up and puting new exaust on it...but i dont know if that will help...and im have other problems...i need to get the timing set right and i was driving down the road the other day and all of a sudden the hole truck started bouncing and when i stoped at a red light it was shaking really bad....i dont know what the deal is....could it b that the the orignal engin was a 305 and we converted it 2 a 350?

thanks....i need help badly

I doubt the exhaust will help with the emissions test. Dont know about the rest.