Custom bugs and buses will do an exchange box for just over $1700.00. Sound good but A bit out of my price range.

http://cbbvw.com/product/18/Reconditioned-T1-IRS 

If you find any others please let me know as I am on the lookout as well.

Given the amount of labour involved I'd say that $1700 is pretty fair. I've never gotten one done either though.