Hello, and welcome!
In order to support macppc back in 2003, endianness was revised for the driver. You may want to review the CVS logs for the driver (sys/dev/pci/bktr/*) if you have not already done so, and you might consider posting to either hppa@ or to tech@ regarding your development effort.
If you've not used the mailing lists before, tech@ is the place to post your patches for review/comment, while hppa@ would be the place to discuss PA-RISC architectural concerns.
http://www.openbsd.org/mail.html