What got me started down the whole acoustic modelling rabbit-hole was trying to scale a D whistle down to Bb. I tried simple multiplication. I got a nice little whistle out of it, but only because I started out with the holes drilled way smaller than my predictions, intending to enlarge them; the whistle was in pretty good tune with these way smaller holes, so I left them that way.

Not everything is linear in frequency. The bore diameter, for example, varies with the inverse of frequency to the power of 5/6. See

viewtopic.php?f=1&t=84789&start=45#p1045576. For hole position and diameter, you might get away with Terry's suggestion. Because D to Eb isn't a big step, you might get in the right neighbourhood if you divide the dimensions by 1.06.