You may already have a Famicom to NES converter, you just don't know it yet!
Yea! More near useless NES tech info.
Anybody out there need a converter to play Famicom carts in an NES for whatever reason? Go grab some of your old first party first gen NES carts like Gyromite. For whatever reason, the very first NES carts made were famicom boards stuffed into an american casing with a converter. I guess they didn't have time before launch to start producing propper NES boards. Open one up and take a look, if you so desire.