Regardless of the makers intention, every rifle is an individual. Even identical guns of the same model from the same maker may perform differently. Some group just fine with either balls or conicals, there's no good way of telling but by shooting them. Still, a slow twist such as 1-60 or 1-66 is best for balls and may never do well with conicals (R.E.A.L, Maxi-Balls, sabots, etc).
The long barreled rifles with the narrow well curved buttplates can be shot from the usual position on the shoulder but were intended for high up on the arm. As we moved west and went to more powerful guns, some were still made that way but we returned to the wide flat 'shotgun' style butts. Even into the 1900s some powerful cartridge rifles were made with the curved butts but had a reputation as 'hard kickers'. Teddy Roosevelt ordered a pair of such rifles but specified that they were to have 'shotgun' buttplates instead.
I have a pair of rifles which appear identical except for the butt. I was using 90 grains of black powder and a conical bullet in one and was comfortable. In the other which has a narrow curved butt, 70 grains and a ball (which is lighter than the conical) was the most I wanted to go with that one, more was uncomfortable. But then, some people aren't bothered by such.
ALSO, If you want to hunt with it, first check your hunting regulations. Many States require a certain bore size. Some States require at least 45 caliber for deer. One State says for elk, 54 if using a ball but 50 is ok if using a conical of at least xyz weight.
Check out Gun Broker and PennWoods, there is also the 'for sale' section here on this website.
Go with a 'double set' trigger as so many single ones are poor to awful.
Get a ball puller before the first time you go shooting. Bullet patches, buy pillow ticking from Wal-Mart. Patch lube, I use a hand cleaner, think it's Perma-tex. If you gun has a wooden rod, get a synthetic or aluminum one and use that. Sometimes people break the wood rods and the rod goes through their hand. Get a bullet starter. I just buy balls now, I don't bother to cast except for specialty stuff. THE TIPS AND FITTINGS ON RODS CAN COME OFF. That can leave a tight cloth or bullet puller down in the barrel, another reason to use a synthetic rod.
NEVER LEAN OVER THE MUZZLE. Learn to load and anything else without putting face or other parts over the muzzle. Try to hold the rod such that if the gun were to go off while you are loading that the rod will cause the least damage to your hand. ALWAYS WEAR EYE PROTECTION.
Shoot and have fun.