What I did to jump up in weight when I got my 68# longbow was to draw it past my normal anchor, almost to my ear, starting with 10 or 12 reps. I moved up in reps as I got more comfortable and now that I have my strength where I want it to be, I just shoot it
I was previously shooting a 55# bow, which was getting to be where it felt too light and it was taking me what I felt was too long at anchor to get what I like to feel in terms of back tension, and 61# was what felt perfect to me as far as the tension achieved at full draw for my best shooting. I thought, then, that 68# would be a piece of cake...wrong! It was a struggle to get it back to full draw after several shots. So I went through this routine, and believe it or not, it was less than a week before I felt totally comfortable drawing and holding the bow.
My newest bow will be 71#, and I think it should be fine since working up to the 68# was so easy using this method.
Good luck!
Craig