the valves are in the block on the k241,its a flat head engine.im not sure why you want to port out the passages but on a fairly stock engine,just polishing the ports will help flow and get you a little more ump.the tractor in my avitar has polished ports,milled head,open exhaust and carb adjusted to match.its also bored 060 over.all this was done years ago and the tractor still runs strong.
Well first go to this thred, http://www.mytractorforum.com/showthread.php?t=48120 and follow the link for the downloadable manual for your engine. Before you can get more power out of your engine, you need to learn how it works, and how to get it to run as new. After that you can learn how to mod them, and you will have a true baseline to what you have done. After that, study up on the art of making power out of a flathead engine. Things dont always work the way we have learned working on newer style overhead valve engines.