It seems like it would be an important detail but my Chiltons and Motor manuals don't even mention it. I have a 77 Service manual for the 425 but it doesn't seem to have a double groove bearing. I would have guessed that the double groove bearing would go in the rear but my logic may be completely backward. You might try posting this in the 472 500 section; there are a few experts that check in there quite regularly. You might even find the answer by Googling. I always use Google to search forums anyway instead of using the forum search function.