Are you sure you want to chop it 4"? My 31 has a 3" inch chop and there were definitely challenges in configuring a comfortable seat that would still allow me to see out the windshield and see the stop lights that are mounted relatively high.

Also, that 3" chop put the windshield wiper motor directly in my line of sight and is still an issue I'm working on.

If you'd like to see what the 31 looks like with a 3" inch chop, check it out at http://photos.yahoo.com/lesbateman31

Good luck with your project.