Whew!

Having left the bow unstrung, the crack closed and became virtually invisible, I felt this was a good sign.
I clamped the bow in the vice with some rubber strapping tied just below the crack so that I could bind it tight very quickly. I flexed the bow to open the crack and flooded it with low viscosity superglue. The  pressure was then reversed to close the gap and the rubber bound round tight.
The strapping came off after a couple of hours, I had to sand it off in places where the rubber has stuck. The hickory back has been thinned and rounded substantially at the edges to try to weaken it a tad the theory being that the load should be evenly spread between back and belly.
I've strung it and flexed it this morning, the draw weight is nicely manageable, but prob lower than I'd hoped.
I'll get some horn nocks on it and hopefully try it out tomorrow.

Update:- The draw weight is a bit low 62# at 28" and about 68# at 30",  I've had it on the tiller, pulling it dynamically and shot it at both 28" and 30" draw. It seems what is technically known as bloody fast but I'll have to shoot it through the chronometer. In actual fact it's probably a fairly sensible weight for me and the fact that it can be flashed back to 30" for flight could be interesting.
The flat back feels nasty in the hand and I'll build it up with something, either wood or leather. Maybe some Yew sapwood.
Anyhow, it's been a good learning experience and a cautionary tale that rushing a bow will almost certainly guarantee you come in under weight.
Update2:- Been shooting it through the chrono', it's about 170 fps which is pretty good. The early cautious shots, prob at 27" draw were about 160. Then I got some consistent readings around 170.
You may wonder why so vague, but it's surprisingly hard to get good consistent readings, I got one over 500 fps and one at 179, They were both miss-reads. The problem is the flexing of the arrow (not such a problem with a modern target bow or a crossbow. It can happen that the middle of the shaft triggers the first optical sensor then the point triggers the second, this would give an unrealistic high reading. Maybe it would be better with the chrono' high up about 30" in front of the bow. There isn't convenient room in the garage to set it up like that with suitable lighting and backstop. maybe I'll try to do it sometime. Better to set it up out doors in daylight, then I'd just need the backstop.