Hi Macca88,
I opened all the records for Harry McKay on the Ellis Island site, and he appeared to be 5'6" about 140lbs approx, but if he sailed from Liverpool he was English, if he sailed from Glasgow he was Scottish. Not sure if that is his declaration, or Ships records input wrong. The first sailings were when he was 17 and these were from Liverpool, maybe a clue to where he was living at the time.
Tom