Yes you can run the 26 head on the 25. You will need to have the head stud holes in the block tapped out as the 26 uses a larger diameter head bolt/stud.
You will also need to change your complete intake assembly and the exhaust manifold. Both hot and cold sides use a different bolt pattern to the 25.
Or, You could do as I and others have done and get a solid lifter conversion for your 25 head. do that and you have a "26 head" that takes all your 25 gear.