I have been thinking about doing this mod (there are several threads about 450 shocks and A-arm kits here on Banshee HQ) simply due to the cost savings. You do need to grind off some metal on your stock A-arms and from what I hear you will put extra stress on the bearings. I think your best bet is to save up your money and get some Elka's or Fox floats of you want a smooth ride.
First you should get a real rear skid plate as the stock one is going to be trashed in no time!!