The 23-year-old, who doubles as a back row, was rewarded for his outstanding form this season by being one of eight Ulstermen included in the Irish squad to tour the "Land of the Rising Sun" next month.
The former Ireland Under-21 captain has become a focal point of the Ulster pack, being one of eleven players to feature in all six of the province's Heineken Cup Pool Six ties in 2004/05.
Having penned a new four-year contract with Ulster last season, McCullough was pipped at the post by flanker Neil Best for the Bank of Ireland Ulster Player of the Year award last week.
"Going to Japan is a brilliant opportunity and hopefully I will be involved on the pitch and play a Test, but there is a lot of hard work to be done before going out there," McCullough told the Belfast Telegraph.
"For me it is a chance to show what I am capable of and to learn a few lessons and I'm looking forward to it. I proved myself at provincial level this year and it will be another step."
"It was great to play with the 'A' team as they were a good bunch of lads and I gained experience," added the Ballymena man.
"I've been involved in the Six Nations squad but realistically this is a chance to get game time and to win my first cap would be a dream come true. I have got to keep making the most of the opportunities I get."There is a lot of talent in Ulster and it will leave rugby in a better state if we can get more established internationals."
The now-retired Gary Longwell was the last Ulster second row to start a Test match for Ireland, against Italy in August 2003.
But with the 6ft 6in McCullough ever-improving, that trend could soon be bucked.