Hey Running Bird, welcome to Traditional archery. After three years of trad, I sold my compound on ****, and havn't looked back.
Before anyone could give you good solid advice, there would be a few question's that would need to be answered.
You have a longbow with a draw weight of 55#@28". Ok what is your draw length?
How your riser is constructed is very important also. Is your riser cut to center, past center, or before center?
The best place to start is to ask your bower what spine he would reccommend. Or, order a test kit, consisting of six arrows cut 1/2" apart.
You will need to decide on how much weight you want up front. It will help alot when tuning your arrows to your bow if you have a target weight. You do this by deciding, weather you are going to be a target shooter, or a hunter. If a hunter, then what are you going to primarily hunt. The rest is common sense.
Once you have the answers to all the above, you will need to know how to make decisions based on that criteria.
Find out the answers, and post them and I'm very sure these guys will steer you in the right direction.
For carbons, I shoot GT Traditional. They are a no non-sense shaft, and as good as they get.
Also, how did you arrive at a 55# longbow? I started out with a 55#@28", and in three months was down to 45 to 48# bows, with 46# being my magic number.