1969 C/10 won't stay running

[Stephen717]

Hi, I know that this has already been covered before but I don't know where else to turn. Three days before my eighteenth birthday I bought my first truck, a 1969 Chevy C/10. It has a 250 inline 6 from a 1979 and a rochester monojet from a 1973 pontiac, along with a muffler from a kia so it is surprisingly quiet. When I bought the truck for $700 I thought that I was getting a steal since I thought all it needed was a fuel pump to be a running project. It has a 3 speed column shifter that is original to the truck but it originally had a v8 in it (I am thinking a 307). Anyway to get back on topic I put the new fuel pump on and checked the points only to find that they were brand new and already set right. it had a slight miss to it but my father and I advanced the timing and rebuilt the old single barrel carb and that took care of that. Then I turned the manual choke (opening thing?) around so that to choke it I pull the choke rod out instead of push it in. Then I replaced the dimmer switch and sprayed some pb blaster in the original horn a few times and rapped on it a couple times with a rubber mallet to get it working again. Anyway I know that I keep getting off topic but my mind keeps reminding me of what I have done and what I still need to do, Like get new side marker lights and replace the interior roof sheet metal. But we got the truck running good and it ran fine for about a half an hour. then I was to to rev it up and see if it would come back to idle. Well I did just that and it did come back to idle but ever since then it has blown a greyish smoke from the exhaust and shuts off when ever it gets to it's running temperature of about 190. its holding oil and the exhaust doesn't smell of burnt oil when the exhaust starts blowing out its smoke but I don't know what this could be and as I said at the begining of this I don't know where else to turn or what else to do. If anyone can help me out with this that would be great.

Thanks,
Stephen