Leaky Slant 6

I rebuilt my slant 6 and I have continued to have an oil leak that I cannot get ride of. On the passenger side of the block the oil is running down the side of the block under the head. I have replaced the head gasket with in 1000 miles of the rebuild with no improvement. Any ideas or suggestions (different brand head gasket other then felpro, etc?). I am running a '72 block with an '82 hydraulic cylinder head.

Matt