Biggest engine to fit in a C

I mostly frequent the pulling site but came across a project tractor. It is a Farmall C over at my neighbors that looks to have been sitting for a while. I am going to see if he wants to part with it. I have a small farm that I need a tractor to pull haybales to the cattle, run a small sprayer and a small shredder. What is the biggest engine I can put in the C. I know it is the F12 and ABC series and 100 200. What about a 240 how big is this engine?
Heard a 504 would fit, how big is that one. dont get me wrong, this tractor will see a track and a sled but there will be more uses than that. I already have an H that is strictly a puller Thanks guys.

Also found some posts that said the 203 motor bolts directly into the C is that true or does it require some work? that is a big power jump from the dinky original engine to the combine engine.

from pics it looks like the 504 c153 motor also mounted to side rails in the front of the engine. Does the 203 combine engine have a spot on the block for mounting to side rails. I think it would be neat to have a C with side rails on it if it could be figured out. also help make a sturdy tractor.

seems that the place to start would be with a 203 engine swap. I saw it was rated at like 50 horses in the combine.

I believe the 504 is the same block, just no sleeves, but the 504 wasn't exactly what people would call a power house. Gutless wonder is what I hear most people say.