In Kubota's Operator's Manual for the FELs LA555/LA805/LA1055, the LA1055 is shown as available on the
L4760,
L5060,
L5460 &
L6060.
For the
L4060 only the LA805 is shown as available.
Note that dimensions for
L4060 are 121.5' X 66.5"; for
L4760 are 126" X 67.3", so it is unlikely the LA1055 is dimensioned to fit the frame of an
L4060.
There would also be the question of front end strength of L4060 versus heavier L4760.
You will have to move up to the larger framed
L4760 to get an LA1055 FEL.
I have an LA805, paired with the optional L2296 Heavy-duty, Round-Back Bucket, on my
L3560. It is a strong combination.
If you are truly moving up from a Deere 420 Lawn & Garden tractor I would not get hung up on the difference between the LA805 and LA1055 FELs. You really need to have a 50% increase in lift before you get a
WOW! difference when operating.
I have had air in the rear Industrial Tires on all three of my tractors as I run over people's lawns regularly. With air in the rear tires, rather than liquid, I need to mount a counter-balancing implement on the Three Point Hitch before I accomplish near-max lifts (Photo #2, #3), otherwise the rear end lifts, instead of the FEL load. With moderate lifts, including a full bucket of Florida sandy-loam, rear
ballast is not absolutely necessary but rear ballast takes strain off the front axle and front bearings. Quite often I use an ETA Cultipacker as ballast (Photo #1). It is heavy and compact. Other times I utilize a Bush Hog (brand) Rollover Box Blade (Photos #2,#3,#4).
{Above assumes level ground.}