i have a 1966 ford 352FE big block, i changed the manifoild gasket and when i put it back together it did'nt run right and now i have gas in my oil.  ???????????  

There are only two undeliberate ways for gas to get into your oil, through the carb or through the fuel pump.  If you carburetor is dumping in so much fuel that it can not burn it then it will get by the rings and soak into the oil, it takes a lot for this to be noticable and the engine usually won't start due to flooding.  A bad fuel pump on the other hand if it has a hole in the diaphram will allow gas to enter the crankcase through the timing cover.

I am guessing you mean "intake" manifold. If the gasket doesn't seat right you could end up sucking water into the combustion chamber and ultimately some will get around the rings and into the oil or cause the intake to suck air from the lifter valley.  Either way the engine will not run right but usually will not cause fuel to go into the oil in any great amounts because the vacuum is into the combustion chamber and not the lifer valley.

So if it is related to the gasket change it is probably in the carb with the needle not seating properly. Otherwise it is probably coincedence.