The Ulster pair, just two of the eight uncapped players on tour with the Niall O'Donovan-led Irish, are both just 23 and have come to the fore for their province in the last two seasons.
Lock McCullough is a former Ireland Under-21 captain and played 22 times for Ulster this past season, scoring one try. Wilson, a tigerish number 8, who scooped the Ulster Player of the Year award last year, lined out 18 times for Ulster in 2004/05, with an untimely ankle injury robbing him of a potential first Ireland cap against the US Eagles last November.
R.B.A.I-educated Wilson, who is set to carry on a proud family tradition as his grandfather Harry McKibbin and his two uncles, Harry Jnr and Alistair have represented Ireland at the highest level, said: "Training had gone really well for me during camp and it was a case of keeping the head down and working hard.
"When the team was read out it took a moment for it to sink in, but after the initial excitement the reality of the job at hand took over.
A former cricket and golf schools champion, McCullough said: "Like Roger, I was delighted when I heard my name read out. The competition for places has been excellent and Niall (O'Donovan) has tried a couple of combinations during training, so I was delighted to get the nod.
"My focus now is to try and do a job to the best of my ability and hopefully contribute to a win on Sunday against a tough Japanese team."
Both McCullough and Wilson started in March's 15-9 win for Ireland 'A' over France 'A'. Four other starters from that Donnybrook game - Tommy Bowe, Anthony Horgan, Simon Best and Alan Quinlan - are included in O'Donovan's XV for Osaka this weekend.