I don't know of anyone who has tore into a K-series enough to answer that cam question, but I would imagine you wouldn't be able to. Valve springs are one thing, cam and head castings are another.

As for the pistons, a couple things come into effect besides just bore size. Depending on the stroke length and the rod/stroke ratio will tell you whether the piston skirt is too long or not. If it is, then you would have to look into having the piston skirts cut to length.