timing chaing cover replcement

Anyone have any ideas s to how to replace a timing chain cover on a 225 /6 without removing the oil pan? The problem I have is that the rubber gasket on the cover base is too thick to compress enough to make the locating dowels line up with the holes.

I posed this question on the slant six forum and received answers from people who felt that the pan had to be removed and someone who said he removed and replaced a cover without removing the pan.

Do you think using a thinner rubber gasket would work?

thanks

Dan