That's interesting that you are able to get the big filter to fit. Can you get a pic of how you have the adapter clocked so it all fits? I put a 340 and 727 out of a 73 Dart Sport into a 65 Barracuda that I threw together as a beater years ago. I always liked the 51515 filters, but had to use a little short one because the way the adapter was clocked from the factory on that 340, it hit the frame rail. I didn't want to move the adapter because it wasn't leaking, so I just used a shorty filter.