Ap1 ballast has 4 screws holding it in place on the AP1 headlight housing.
AP2 ballast has 3 screws holding it in place on the AP2 headlight housing.
Mouting it on, I presume would just be a matter of getting some metal stripping long enough to cover the ballast, and wrap around the underside of the housing. Then gluing the metal striping to the plastic AP2 headlight under housing section with some form of Dynagrip / Permatex glue.
Or you can save yourself alot of hassle and just buy the AP2 ballasts etc and just screw them straight in :p