I would recommend against this. A 6" wheel is likely to be rated for lower speeds than your 4 1/2" grinder, the wheel will be closer to your fingers and if it explodes it will be unpleasant. Gloves won't do a great deal for you if it kicks and your hand slams into the wheel. Better to use the tools you have safely, take a bit longer and enjoy the finished product than injure yourself and have a half finished project.
Looking forward to your progress however. I already have an anvil but am going to make a post anvil soon. I have to steel, just need to shape and heat treat.
I find it hard to believe that this advice was given at all, if you have ever seen a disc explode it is really ugly. Guards are designed for a reason.