The flange focal distance for the canon FD mount is shorter than the pentax (
Lens mount - Wikipedia, the free encyclopedia ) and so you are highly unlikely to be able to focus to infinity no mater how you mount it. If the rear lens group is small enough it may be possible to make a special mount for it so that it is just inside the camera without fouling the mirror but unless you have a particularly special lens it is probably not worth tye hastle.