I have an Excel spreadsheet made up for my previous airplane, a '73 P337G. You would have to plug in your empty weight an moment, and I would have to explain how to use it to you. No warranty of correctness from me, please run manual W&B to compare with the spreadsheet results. Call me at 503-693-7266 and I can email you a copy. I would like to speak to you first though.
Kevin Mackenzie
webmaster@337skymaster.com