Oh I see, sorry, I misunderstood your request. You're right, target notetags work on Skills and Items only, there isn't an option for Equipment and Weapons.
knuckles and claws add hits to physical attacks
If by "adding hits to phisical attack" you mean raising the ATK parameter, you can use <equip atk: +x>.
heavy armor reduces targets and/or hits from physical skills
To reduce hits you could raise evasion, same notetag as above, except change
atk to
eva.
No idea how you could impact targeting though.
Sorry I cannot be of more help D: