Tommy,
Is your Bess a 12 gauge cylinder bore? If it is, you might try 70 grains of 2f with equal volume of #5 shot for squirrel - try it on a target first of course, you'll want to know if there are any big holes in your pattern.
If the pattern does have holes you can increase the amount of shot, say, 80 grains' volume equivalent to the 70 grains of powder. You will need to experiment a little bit to see what will work for your gun.
You might not need quite that much powder to kill a squirrel, but you might need it to pattern well (my experience). My son killed his first few squirrels with 45 grains of 3f Swiss out of a little .56 smoothbore. That was a marginal load but effective at 25 yards or so.
For rabbits you can use less powder, I use 60 grains in a 12 gauge with slightly more volume equivalent #5 shot.
I like the 1/2" fiber cushion wads, your mileage may vary (we use Wonder Wads in the little .56's). It's fun to experiment. I soak the cushion wads in melted Crisco shortening, wipe them off with a paper towel and store them in a little baggie before use.
Please do post your progress and results, I for one am very interested in smoothbore shooting.
What kind of fowler do you have on order?
Mark