Historic rude cruck blades, purlins, ridge and tie beams are generally made from boxed heart materials and hence the dimensions quoted above are for the typical round stock needed prior to conversion to boxed heart. Cruck blades can be found with lots of waney edge and are quite variable in their profile with mixtures of different shapes (elbowed, ogee, straight, etc.) scribed together to form the cross frames. Differing cruck profiles result in cross frames that do not necessarily provide an even platform for running side purlins & ridge and this can give rise to difficulties in providing a location for wind brace foot mortices so sometimes it's necessary to add blocking pieces and / or struts as required to make the frame geometry work.
Our elms died out in a major way back in the 1970's but as you mention above left alone they will grow back from suckers springing from the rootstock (not the stool). In turn these trees have started to die back again after 25-30 years regrowth but by this time they had already put on sufficient girth and height to provide sufficient stock to hew out one good purlin from same. After examining 5-600 year old elm frame components I think that there is every reason to believe that Dutch elm disease is not a new phenomenon and that the medieval carpenters were maybe just making the best possible use of available timber stock during phases of elm die back.
I will try to remember to take a few photos of the elm growing in our woodlot.