The Electronic Fleck Valves ( 5600SE, SXT, 6600, 6700, etc ) use Special Valve Bodies and matching Special Main Piston Assemblies.
And the 3456PSKIT will not work to rebuild the 5600SE valve ( or SXT, or 6600, or 6700 ) because the piston with that kit is different than the one used for the Electronically controlled valves..
However, the Seals and Spacers and the Brine Valve Piston are the same (see below).
And we do have an SXT KIT ( 60102-71, 60125, 60032 ).
The piston can either be the Downflow with GREEN End Plug 60102-71
Or the Upflow with Oval Linkage instead of Triangle 60102-62
The Seals and Spacers Kit is the same:
And the Brine Valve Piston is the same:
For other parts available for the 5600SE and other "Electronic" Fleck Valves,
Search List 5600SE parts
Fleck 5600SE shown below,
Fleck 5600SXT shown below,
Fleck 6600 shown below,
Fleck 6700 shown below,