JOHN Ryan of Gunne estate agency is quoting a guideline price of £600,000-plus for The Oak Tavern, a large retail licensed premises at Northside Shopping Centre, Coolock, Dublin 5, which is to be auctioned on April 17th. The 9,500-square-foot premises are held under a 35-year lease from 1975 at an annual rent of £78,000 per annum but the new owner will have the option of buy out the freehold interest. The business had a nett turnover £1.3 million in the 12 months up July, 1996.