GPx 600r 86-89. Need engine or parts.

hi, i have just sourced a GPX 600r probably 86-89 (black and grey in colour) for $300 unregistered. I want some advice as this bike has a 20 cents sized hole on the top of the gearbox and the last owner said it just locked up. I have spun the motor over and it still turns but i was wondering if i would be better off to buy a 2nd hand motor and gearbox and drop it in or recon the old one and fix the g/box. I live in WA and have no contacts for parts or spares so any help would be greatful. Its a classic bike and would like to restore it to its former glory. I also need an ign barrel and tank barrel and seat barrel as the previous owner lost the keys. Also a workshop manual. Any help would be great. Cheers.