Well, if you're hoping to take dimensions off of a merged isometric, you'll find the numbers wrong. That's because an isometric projection uses an isometric scale, not a true scale. Happily, the two are related by the simple formula:
isometric scale = (sqrt (2/3)) x true scale
Solving for true scale:
true scale = ((2/3)^(-1/2)) x isometric scale = 122.4745% x isometric scale
In practice, this means that you can use HighDesign's scaling tool on a selected object, scaling it by 122.4745%, to get an isometric you can pull dimensions off of.