The thought had clearly eluded the difficult-to-beat goalkeeper in the suddenness of his emergence as Ruud Gullit's first-choice saviour. "Yeah," he said, pondering the significance of his expected Wembley selection, "it would be my first FA Cup start for Newcastle... There you go."
If the most secret of the weapons with whom Gullit hopes to slay the Old Trafford Goliaths was momentarily struggling to come to terms with his dramatically elevated station in football life, it was perfectly understandable.
When Newcastle lost to Arsenal in last year's final, Harper was beneath the twin towers as a member of the Toon Army. He was the club's fourth- choice goalkeeper behind Shay Given, Shaka Hislop and Pavel Srnicek.
Not until last November, seven years after his youth team debut (and three years after his actual League debut, on-loan to Bradford City), did he make his first senior appearance for Newcastle - as a second-half replacement for the injured Given in a 3-1 win against Wimbledon at St James' Park. And only in the final three matches of the Premiership season has the 25-year-old finally claimed the number one spot on the Newcastle team sheet, albeit as the wearer of the No 13 shirt.
Given's collywobbled kicking against Spurs in the semi-final and gifted goal to Everton's on-loan Kevin Campbell in Newcastle's next match gave his elder understudy a chance he has grasped with both hands. In Newcastle's stuttering run-up to Wembley, Harper has been Newcastle's most impressive, most assured performer.
Against Blackburn at St James' Park last Sunday he produced two blinding second-half saves to thwart Jason Wilcox and Lee Carsley. He also produced the kick of the game, coolly volleying up field when placed under pressure by Rovers. It was no surprise when he was offered, and duly signed, a new three-year contract in midweek. It would be a surprise if Gullit left him on the bench today though Harper has been careful to add the rider "if selected" to his Cup final comments this week.
"I don't know officially, so I don't want to take anything for granted," he said, refusing to count chickens in the Magpie Room at St James' Park. "But obviously I'll be very disappointed if I'm not in the team."
Harper's breakthrough at Newcastle has been a long time coming though. Having signed as a trainee in 1991 and then as a professional two years later, he is the second longest-serving player at the club, behind the centre-half Steve Howey.
Though he has yet to line up from the start in an FA Cup tie for Newcastle, he is not without experience in the competition. He made a substitute appearance in Newcastle's third-round win against Crystal Palace in January, after Given was sent off, and played in two ties while on loan to Huddersfield last season, distinguishing himself in the Yorkshire Terriers' fourth- round defeat against Wimbledon.
His save from a Marcus Gayle header, highlighted on Match of the Day, was reminiscent of the Gordon Banks classic against Pele in Guadalajara, which was rather appropriate. Asked to select his all-time world XI in the match programme that day, Harper picked Pele as his one substitute and 11 members of the Half Moon pub team from his home village, Easington, on the East Durham coast.
"I was their manager," he offered by way of explanation. "There were some good footballers in that team, but I didn't seem to bring the best out of them."
It was as a goal-scoring centre forward in the Easington Comprehensive School side that Harper started bringing the best out of himself. He scored a hat-trick when an Ipswich scout came to see him and had trials at Portman Road. He then switched to centre-half and had trials with Sheffield Wednesday.
"I started up front and worked my way backwards," he said, chuckling. "It wasn't until I was 15 that I played in goal. The school team keeper got injured and I stood in for him. And here I am now."
Harper's path to Wembley has indeed bordered on the bizarre. He arrives today to line up opposite Manchester United's departing Danish international Peter Schmeichel, whom he describes without any sign of affectation as "the greatest goalkeeper in history," having faced just one penalty at first-team level for his club.
He has yet to let one in either, having touched Jeff Kenna's kick on to his right-hand post at Ewood Park last December, though he was beaten from the spot in Huddersfield's home defeat against Sunderland last season. "I thought Kevin Phillips was going to take it," he recalled, "but Allan Johnston did."
Guessing right could be vital this afternoon, with penalties scheduled to decide the final for the first time should the two teams still be level after extra time.
"I've only been in a penalty shoot-out once before when I was 17," Harper said. "I was playing in goal for East Durham Community College. "I scored, actually. I took the first kick. We still lost, though.
"We've been practising this week but, to be honest, if it comes to that it'll be a lottery really. We'll be trying to win it before penalties.
"We know it's not going to be easy, especially for whoever is picked to play at the back. People keep saying, `Is Alex Ferguson going to play Yorke or Cole or Solskjaer or Sheringham ?' It's a problem any manager would settle for.
"I faced Andy Cole a lot in training when he was here, but never from the penalty spot. He was too busy putting them in from all angles. But it'll be difficult for us, whoever they have up front. We've just got to go all out, and hopefully be at our best."
Not that Harper was at his best on his own turf in Easington on Monday: "I was in the garden cutting the grass," he said, "and complained about a bad back to my next door neighbour. He said, `Aye, it'll be a lot worse than that on Saturday.' ...He's a Sunderland supporter."