<font color=blue>...72" blade that mounts using the 4 pins the bucket uses (about 3 min. to change) for $1220...</font color=blue>
Your JD4300 will accept a real front blade with full hydraulic angling for around $1500, I believe. Same width, but you take off the FEL and mount the blade to its own under-chassis mounting system. Having the hydraulic angling would be well worth the extra $200-300 to me. And I'm told, but don't know for sure, that you can push a lot better with this arrangement because it's a straight push right against the tractor frame.
I have one on mine, and it's great. But, I don't have a fel, so I don't have to hassle with switching them. Your solution would be easier on and off, but the lack of angling would be a royal pain in snow.. at least IMHO. I had a GT235 that I used to push snow with, and I had to keep getting off and manually adjusting the blade angle. That was a hassle.. I can only imagine how much of a hassle it would be to not be able to adjust the angle at all.
hth,
Bob