I frequently build a bow to full draw or nearly full draw with the intention to shorten it. Allows me the opportunity to get good tiller with the least amount of wood fatigue. But I'm not in a rush to get a bow finished, on the contrary the experience is what I'm after. I have probably fooled myself, but I think a better bow results. I believe this techinique is mentioned in Toxophilus.
Tiller it like you want the finished bow. If you shorten it, that will have a tendancy to stiffen the outer limbs. Draw weight is only limited by the quality of the wood, and one's craftsmanship. For 26" draw, 70# or 80#, at 68" and 72" respectively, would not be out of the question IMHO. But I've only made 2 or 3 black locust bows. For 26" draw, I would not go for full compass unless you get down to 66" or shorter and/or what a ton of draw weight.