Thanks to all for the replies. Right now, I have 2 cm of spacers above the stem, and I shall go the hacksaw route with appropriate blade guide. I like mechBgon's method of finishing the cut with a nice chamfer, and yes the "measure twice, cut once" will be observed, or fork for 52 cm frame will be advertised.

Although the pipe/tubing cutter can be used if the "feed rate" is slow, it displaces material (not removing). It seems some have luck and in my experience with cutting copper tubing, it does produce an external lip (but not an external lip).

Again thanks for all the good replies. This topic isn't as hot as "best chain lube" but did get more responses than I'd imagine!