Any advice would be greatly appreciated.
I'll give you
any advice, but can't guarantee it's
good advice
The difference between 55# @ 26" and @ 28" won't be much. You won't have to scrape much wood to reach that draw length. The trick will be making sure you keep the tiller good. Without seeing what we're starting with it's hard to get more precise.
As for backing it with fiberglass... Hickory is pretty darn tough, especially in tension. Therefore, I highly doubt it would need a backing
unless the grain on the back is severely violated or the limbs too narrow.
To change the brace height... if your string is tied on to one end of the bow and has a loop on the other end, then you can shorten the string by adjusting the location of the knot. If it is a continuous loop string, then there's not much you can do (you can add some twist but I doubt it'll make a big difference). Personally, I prefer a 5" - 6" brace height measured from the neutral plane (middle of working limb). Too low and it'll slap your arm, too high and it puts too much stress on the limbs.
Hope this helps in any way, and WELCOME!