I, too, had to join the ranks of the LA463 QA owners, and armed with info from Tractorbynet, was able to gather some additional info.
The first dealer I spoke with promised me that the QA available now with the LA463-1 was not available for the LA463. Apparently, Kubota will not sell the unit separately. That dealer also promised me that the L2230A was only for the LA513 loader, and then attempted to upsell me on the ATI QA for over $700. But a cross reference from a truly awesome dealer indicated that the L2230A uses all of the same part numbers as the QA included with the LA463-1, so it is the same except for the label. I have heard only great things about ATI QA's, but preferred to stick with Kubota and save some cash. According to the 2007 pricing lists posted here on bynet, the list price of the L2230A is $381, and according to the LA513 parts manual, weighs 165 lbs.
One possible reason for Kubota not endorsing the L2230A for retrofitting a LA463, is that according to their -build my kubota- section on their web site, there is a suggested $501 price increase from the standard LA463 (with bucket) to the LA463-1 (with bucket), so if you bought the LA463 and then added the L2230A and the L2256 bucket you would only pay $37 more and get 2 buckets. Not that you'd want two, but it looks like a better value.
Another reason may be that kubota has provided a capacity increase to accommodate the weight of the quick attach. But I was unable to find any published specifications as to any capacity increases during my research. If anyone has the specs, specifcally for the LA463-1, I would be curious to see them.
As far as bucket options, the new standard is a 66 inch bucket: the L2256. It is listed as 38 lbs lighter than the 60 inch included with the LA463, and with the exact same cu. capacities. All of the weld on brackets I saw to retrofit my original bucket were around 100lbs. Add the 165 lb QA, the extra 38 lbs of the bucket and a weld on bracket, and you get to 300+ lbs. less capacity than you are used to. Seems like a lot for the LA463. Plus the 4 extension of the QA and the OEM 60 in. bucket is a few inches deeper, putting the cutting edge 6 or so inches further out than you're used to. As a result, I would expect a tangilbe reduction in lift and breakout capacity. Also you get a standard skidsteer rollback and dump angle with the new bucket; the old bucket retrofitted may have some limitations because the buckets back angle that the weld on bracket is on is not standard skidsteer. (or at least not what Kubota specs for the QA bucket on the LA463-1)
Disclaimer: these numbers are based on what was available to me, so they may be off from actual weights, may be shipping weights or outdated, but there is little doubt that if you feel your LA463 loader has little power to spare, the newer bucket is a better option than a retrofit. Although it seems like people who have done the retro fit have been satisfied.
Retrofitting the original bucket is by far the least expensive route. The 66 lists for $538, but I have seen weld on brackets in the $100 range. Another compatible Kubota bucket is the 60 inch TL2142 used on the
B26. It is also listed at 212 lbs. but has a higher list price of $737 and slightly lower cu. capacity, and if you would spend that much, the ATI 200 series bucket is also a very nice match for the LA463, but MSRP is $800+ (depending on width) and freight.
Hope this helps anyone interested in upgrading their LA463. Good luck!