There may have been an adapter board to allow one to use a 2x3" Graflok rollfilm holder on a 4x5" Graflok back, but it would have to have Graflok slides on it, so that wouldn't be it. A normal 4x5" Graflok back is 4x5" only, but the inserts should be interchangeable with 2x3" Graflok backs, so if you had a 6x9cm 220 back, say for a 4x5" and a 6x9cm 120 back for 2x3", you could probably switch the inserts and shoot 120 or 220 on either camera. I do that with my Linhof rollfilm backs.
Inserts would not be interchangeable, however, among different rollfilm backs, so you couldn't use a 6x6 insert in a 6x9 back or vice versa, because the format mask is part of the shell, and it has to match the format of the insert that winds the film.