i believe you change 'minidb' to 'inventoryDB'
i just tried it out real quick. seems to work. then just assign those items like below to use gold bars and iron bars.
Database:
# Databases Supported:
# Flatfile, FF, mini, minidb
# - These all equate to miniDB
##
# item, items, inventory, inventoryDB
# - These all equate to InventoryDB, which uses inventory for storage
##
# xp, exp, orb, xpdb, expdb, orbdb
# - These all equate to ExperienceDB, which relies on Experience for balance.
##
# mysql, mysqldb
# - These will attempt to connect to MySQL
##
# sqlite, sqlite2, sqlite3, sqlitedb
# - These will attempt to create & connect to SQLite
##
# postgre, postgreSQL, postgreDB
# - These will attempt to connect to PostgreSQL
Type: 'minidb'
# These are for InventoryDB only.
# MajorItem is the item or block ID of the major currency
# MinorItem is the item or block ID of the minor currency
# e.g. MajorItem: 266, MinorItem: 265 for Gold/Iron
MajorItem: 266
MinorItem: 265