Thinking about rebuilding my worn out Th-350 myself, any input on the difficulty about rebuilding it myself? Any special tools required? Thanks

 

I built several 350's in early days without proper facilities in order to have my only basic transportation, so it's doable. 2 things you will need at the very least will be long nose snap-ring pliers designed for auto-tranny use and a compressor to be able to get the low clutch apply piston retainer / return spring assembly compressed without loosing your head or fingers and, of course, re-installed. A feeler guage will be usefull especially if you plan to install other then stock spec. clutch pack {friction / steel } components.
That's the minimum IMO, and a clean work enviroment and parts cleaning facilities is always a major requirement for any AT work.
There's a few more needed tools but those mentioned are pretty much in-despensible and they are not cheap.
This will get you rolling but is by no means what is needed to preform a dependable rebuild. These are just basics I got by on for a whille a few times.