If you are getting the ferry to Belfast, you will need a letter of invitation from the chief constable there, they will want to know the rifle details ammo etc and you will need to send them a copy of your firearms permit (takes a few weeks to process). For the south you will need a European firearms permit, you will need to apply for a temporary southern Ireland firearms permit and a deer hunting licence, if you are going with a guide he will be able to provide the land details etc for the garda. it is pretty straight forward, ive done it a number of times but be warned the southern Ireland Garda wont accept photo copies of your permits and mine have got lost once. Also make sure you allow plenty of time as it is a slow process.