I GMed Harn back in the 80s using classic Runequest, and it was always a bit of a problem with the magic system then. I just used battle magic and ignored Rune magic. Nowadays, If it was me I would use the BRP based Renaissance rules for Alchemy which uses the elements and is very close to the Shek Pvar magic system. There is a free version available somewhere. For anyone who knows Harn, it's the religions that are the real problem!!