Just to finish off the thread with a couple of notes and pics...
The width of my LA463 bucket was 58 3/8" as others here have noted. The toothbar was 1/2" shorter than that, instead of 1/4" as advertised. I used two 1/2" galvanized washers on each side between the toothbar and the side wall to make up the difference.
I drilled my holes in the front of the slot in case I ever need to do the flip into the bucket technique. I installed the toothbar and used a 1/2" center punch to mark the holes, then removed the toothbar. I then drilled a small pilot hole from the inside and stepped the hole up to 1/2" using several intermediate bits from the outside. I did not need to oversize the hole using a larger bit to get it to work (I had them on hand just in case).
I did not weld on the 3/8" plates on the outside, but did install them. I will have them welded later.
Overall, a very easy installation. I used the toothbar to move some logs and dug a hole for fun. That little bit sticking out there allows you to haul a lot more brush in the bucket alone. I can't wait until this summer to see how it digs after the sun has baked the clay soil around here into a layer of rock!
Here are a couple of pictures of the toothbar installed and moving some logs. And yes, I made the ultimate mistake back on day 1 (pic 3)!