Re: Roberts Longboat 21
Welcome aboard Knackers.
I can't help directly but let me say that the very few Roberts Longboat 21s that I have seen have had different sized windows. Some (many?) Longboats were amatuer finished and as such, the plans weren't always followed in detail.
Could you not measure the existing broken windows or even just the hole they were in and go from there?
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence