I have done two engines so far, an AC WC and a continental engine. The parts for a C are readily available so that isn't a big issue. The few extra tools needed (ridge reamer, cylinder hone) aren't terribly expensive. The only thing is the space to keep things organized. And have the proper reference material.
This book is very good on getting you started with the tools needed and a general how-to:How to Rebuild and Restore Farm Tractor Engines
Also the I&T manual and Allis service manual are needed for detailed info on your engine (both available from this site).
Finally this forum has a lot of helpful knowledge on problems and how to solve them.