Oil mist??

[Barney1970 CST]

Hey guys,
I was hoping to get some feedback from you guys about what could possible be going on before I pull the engine and do a rebuild. Heres the story. I have had this truck about a year now and do not drive it very much, it is a 72 C/10 lwb. It has a 350 and 3 on the tree. The PO I got the truck from had the motor rebuilt 2 years before I got the truck, he gave me all the paper work when I got the truck. He sold it to me because he did not drive it much either. I drove the truck around town for the first 6 months and had no problem, it has been sitting in the garage out of the weather the last few months and I start her up and let run for 15 to 20 minutes about once a week. Ok now to the problem, today I started it up and backed it up out the garage and drove to the end of the street and back to the house. I noticed when I got out the truck it was smoking just a little. I put my hand at the end of tail pipe and did not notice anything on my hand. I left the truck running and went to go get a sheet of paper. I put the paper about a 6-8 inches away from the tail pipe and start seeing small black dots on the paper. I wiped it with my finger and it looks like a oily mist. I did the same thing over the passenger side tail pipe and I am see the same thing, but not as bad. It is not what I would call bad out of either side, just a light white looking smoke. It does increase when I hit the throttle. The only thing I did was change the oil in the motor over the winter, and new plugs and wires. I pulled a few of the pugs this afternoon and they are clean, looked over the plug wires to make sure I put them back on in the right firing order and it was correct. What could have happened over the winter? Could it be valve seals? Could it be the rings? The gas has been sitting in the truck for a few months, but that would not make it smoke would it? I will try what ever you guys suggest, I already have new valve seal that I picked up today, I figured I may start there. I have the motor out of my other 70 and hoping to install it this week, I really dont want to have to rebuild this motor also.