I just noticed your “business card thickness” description of the mouth. That should be adequate. At the very least, you should be able to adjust for a shaving thinner than that so that the mouth opening isn’t an issue; however, I think the opening you describe would be adequate no matter what.

Also, once you take care of the jamming issue, inspect the blade width relative to the width of the plane body. On old planes, it is typical for the body to have shrunk. Since steel does not shrink, the blade will be too wide and will not quite match the shape of the bottom, either. So, somewhere along the way, you’ll want to correct this. You can do some work with the plane in that condition, but it isn’t ideal and, for some profiles, the blade hanging out wider than the plane body will lead to gouging that will spoil the profile being cut.