JR Nara station map (including lockers):
http://www.jr-odekake.net/eki/premises.php?id=0620816
Horyuji
http://www.jr-odekake.net/eki/premises.php?id=0620819
Coin locker icon: コインロッカー
Having said that, there are only very small amount of large size lockers. And each use is 600, so 1200 for the 2 stations for each bag.
Meanwhile luggage delivery from airport to your hotel in Kyoto is ~1700 per piece. No need to lug the bags around. They arrive next morning.