You can just order the 460 FULL WRAP piston and adjuster screw. Not much point in getting the standard 460 parts. This upgrade applies equally to the 361 and 441 pumps.
I was going to post pics of the process, but it's exactly the same as the 066/660 upgrade I posted previously.
http://www.arboristsite.com/showthread.php?t=31559
Took me all of 10 minutes including stripping down an old 460 pump with a broken casing.
Like with the 660, the piston is modified in the end cup and shoulder, and the control bolt has a greater eccentricty.
Give your dealer the following part numbers:
Entire HO 460R pump - 1128 640 3250 - $84.50
OR
Upgrade parts:
piston - 1128 647 0602 - $26.20
Control bolt - 1128 647 4803 - $3.90