Andy-several of the guys have replaced the front seats via a 337 with Bonanza seats and a custom mount. I did my interior in 2012 using the old seats and wish I had waited. The Bo seats are more conformable, take up less room and are easier to get in and out at inspection time, etc. I also think a 337 for the back seats should be attainable as well. I put a Baron seat in the back and it fit perfectly and was much roomier with footroom, etc. Dan McLeod and Nels Harding are 2 guys who have done it I believe.