This is the place to get bamboo from
https://www.ukbamboo.com/Apart from what I just googled I don’t know the bows but the dimensions you have listed certainly seem reasonable.
I have found the only way to get a new design to target weight is to make several of them, it’s pretty much impossible to get it roughy first time round. If I were to make one I would start around 65” and if it doesn’t take too much set I would shorten it. Bamboo is cheap and you can buy it in pre cut slats but they may come a little thin.
Looking at photos online there is a variation in sizes and diameters of bamboo so that’s likely why you are finding various dimensions listed. Keep the tips
As narrow as you can and don’t forget to make it with the outside of the bamboo on the belly.