Howzit VA,
Welcome to the forum....
No problem regarding the pulley change size, just watch the diameters/ratio and you should be fine. Try and keep the alt/engine spacing as much as possible to get a decent lap on the alternator pulley to prevent it slipping. Contact your local belting supply guys and they will give you how many belts of what sectional size to transfer the power you need.... Remember, bigger pulleys on both sides mean lower belt tensions, meaning less belt wear.... Particularly handy if you are in the sticks away from the "dorp" and need to travel to get spares!
Cheerz
Ed