Does the three-point hitch category (ISO 730 Cat.1/2/3) affect kit selection?
No. ISO 730 categories define the lower link pin diameter: Cat.0 17 mm, Cat.1 22.4 mm, Cat.2 28.7 mm, Cat.3 37.4 mm. These dimensions belong to the mechanical interface between the implement and the hitch. Since LFT20, LFT54 and ELF-812 connect to the control side and not to the hitch, the category does not determine kit selection; what decides is the cable-operated Lift-O-Matic mechanism.
ISO 730 standardises the connection points and dimensions of the three-point hitch on agricultural wheeled tractors. Besides pin diameters, the spacing between lower link pins also varies with category: approximately 500 mm (Cat.0), 718 mm (Cat.1), 870 mm (Cat.2) and 1010 mm (Cat.3). These numbers determine whether a plough or a seed drill can be attached to the tractor.
Electronic retrofit kits are entirely outside this interface. LFT20 and LFT54 pull the quick lift cable; ELF-812 drives the hydraulic control lever. Neither touches the lower links, the top link or the pins.
Category matters indirectly only on this point: tractors in larger categories generally carry heavier implements, so the force the hydraulic mechanism takes may increase. In that case check the stiffness of the cable and prefer the 15 kg of LFT54 pull force over the 10 kg value of LFT20. The decision still depends on the measured cable resistance, not on the category.
Full topic: Converting a tractor hydraulic lever to electronic control