Thanks Brian,
Thought I'd read the instructions thoroughly but obviously missed that bit. I'm guessing you are Brian Roberts of Imara Blog fame? I have gleaned lots of useful info from your blog and pictures etc.
I found a review that mentioned the lack of mast length measurement, just the distances for attachments which cannot be used to add up and give a mast height. Despite the review saying that it wasn't mentioned and that they scaled up the measurement from the "non-scale" plan, then then did not give away the height that they came up with!!! What height was your mast? If you have deck to top measurement I can work out the below deck bit for myself.
Thanks in anticipation!
Paul.