Attaching the legs to the floats depends
on how the floats are made. Some floats come with mounting tabs
as shown above. In that case just bolt the landing gear legs to
the tabs.
USE SELF_LOCKING NYLON-INSERT NUTS. Don't ask me how I know this,
but it was not pretty. With the T-nose strut above you'd use two
wheel collars on each side, and sandwich the mounting tab. Hold
the wheel collars together with pliers when you secure them. It's
important to grind flats in the axle to accept the setscrews so the
wheel-collars don't slip.
If the floats just have a plywood spine on top, it's effective to get 4
nosewheel blocks and attach them to the tops of the floats. Put the
axles thru the blocks and secure with wheel collars. Again, make
sure these cannot come loose. Again: grind flats into the axles
to accept the setcrew in the wheel-collars

The float leg assembly should be as
rigid as possible. If you are using original wire gear or
if your floats flex when you are cruising through waves it's a good
plan to tie the floats together with Spreader bars. Actually they
should have been named "ANTI-Spreader" bars, but they are horizontal
links between the tops of the floats that brace the assemblies.
Also think about using a drag link from the upper front mount to
the lower rear mount. This keeps the float assembly from
deflecting aft when you hit a wave.