Let me be the first to say, Welcome to APUG!

Are you referring to the Holga 135 or the Holga 120? The image circle provided by the Rokkor will probably not give you much of an image on MF film. Probably the most important thing is to but an MD to something else adaptor, find a way to ensure that the lens flange will be the correct distance to focus on the film plane at infinity (measure or use wax paper where a GG would go). Then all you gotta do is glue the adaptor on and it should work.