Yes, as you suggested, the fenders would have to be changed over to use the 460/461 front grill and head light surrounds. I did end up replacing both fenders this spring as they both had slight damage and it was about the same cost as repair. The 460 fenders do not have the vent openings for the G500 air intakes, so that would add a bit of work. Some of the 461 fenders like the G270, and G280 have a passenger side intake, but it is in a different location than the 463. The bottom line was that it could have been done, but for me it would have required too much fabrication and I am not a welder nor the kind of person that would fork over the amount of extra money to get this done. I could have cut out the recessed openings from the original fenders to graft onto a new 460 or 461 fender, but ended up giving one of the fenders to a friend of mine and just sold the other pretty cheap, so now they are gone.
The old style 460 front end is one of my favorite features of the Pur edition, but I decided I was not going that way for the above reasons. The black 463 trim looks great and is an easy change over that suits my goals for the truck.
The brush guard modification is really easy. The middle bar is already set up for two locations, and the plastic hole plug moves to the other unused hole. Using a tow pin bumper, pulling the pin is a bit awkward with the original placement, but easily done once the middle bar is moved up. I had my brush guard off this morning to put in some LED city light bulbs in the headlights so snapped a couple of pics, including one of an extra upright I have laying around.