First thing is to use powders that are suitable for low load densities. 231 or HP38 come to mind real quick, but I'm sure others can suggest powders as good or possibly better.
You can load the .44 Special loads in the Magnum brass, but velocity may be slightly lower due to the larger case volume, and that can be compensated for by a slightly larger charge. If you have a chronograph, it can guide you to book velocities.
It is not a problem to use .44 Special brass, either. The cartridges have the same relationship as .38 Special/.357 Magnum, in that the shorter cartridges can be fired in the longer chamber.
