I guess if you could get hold of a 14"x6" MJ-PE reducer, Small end MJ (SEMJ) it could go right in one socket of your 14" MJ 45 degree bend (check specific manufacturers of fittings or 3rd party restrainers for possible use on plain end of fitting, if application is pressure and the bend cannot be thrust blocked.) Alternatively, perhaps you could get one 14"x6" MJ wye and simply plug the short end of the run with a 14" MJ plug. In the latter case, I'm sure all manufacturers would universally say their restrainers would work on the ductile iron pipe ends inserted up in the 6" and 14" MJ bells left (at the 45 degree diversion angle you want) and the assembly would thus presumably work unblocked, of course as long as adequate restraint length of piping was provided each way for the application conditions.