Very time consuming, and yes its difficult. The motor has to come apart, drop all the valves and keepers, and then go to work.
It can have some good gains, but you can only go so far without some serious knowledge of what works and what does not. You cannot risk reshaping the ports without the right tools and knowledge, BUT you can smooth things out and improve some flow a bit. Alot of work to just go after that. If it is apart already, then it may be worth the time , if you have the free time and a good steady hand.