Chevrolet: 350 chevy rear oil leak, distributor hole, 350 chevy

Question
I installed a rebuilt 350 V8 (only a few hundred miles on it)into my 1970 chevelle. After running the motor for about a minute or two, motor oil starts leaking toward the rear right of the motor. This motor was previously in another car and was not leaking any oil. At first I thought it was a bad valve cover seal. I replaced the gasket twice but there was no change. With a flashlight, I looked where the engine meets the transmission and it looks like the oil is seeping out somewhere around the top of the bellhousing right below the distributor area. Actually, I'm sure it is coming from somewhere in this general area. Is there something I overlooked when I mated the motor to the transmission? This is only my second engine swap. Please help if you can.

Answer
HEA;
 Oil leak ok , well take a look and see if any oil is comming from the distributor hole , or the intake manifold, or it could be from the rear oil sending unit as some have a hole in the back for a sending unit or a plug and if no unit is there and no plug you got oil comming from it, or if it is comming from in the bellhousing it could be the rear seal, but it might be from a sending unit hole ok check it out.