[OZAPRS] APRS and Codan 8528

[Olsen's Tours and Training]

I've been using my old Codan 8528 as my igate radio on 40m for a while now as my other radios are in use. It can be Rx only until such time as I can get some modifications done. 
I've read of the PS modification and the external selcall/data circuit board, but I can find no real information about them.
Can anyone assist me with what is required - circuit diagrams, interface with radio etc.

David