junk that head gasket, ive heard nothing but bad things about them, a std ford one is more than up to the job, but get a rs one, there about £40.

as for cam, you cannot get std cams anymore, there are the same as xr2i ones anyway so you culd sorce a good s/h one, but tbh, you may as well get as close as poss to std kent or piper ( i reckomend kent though)
the T25 doesnt fit the T2 manifold so im told but i have never tried it but if your not looking for big power stick with the T2, your engine will be like mine when done, but i have a kent cvh35 came and the stage 1 set up with uprated injectors etc but im still using the T2 turbo