Having a 261 with the 848 head is actually kinda cool -- as long as, like Hotrod sez, the head has been modified with the correct steam holes.
I'm running an 848 head on my 261 and I'm very pleased with the performance. I'm not exactly sure if it really adds all that much. But it is fun to brag about it

Now if I could only get the right carburetor ...

John