Not familiar with a "C" Riser... Differant Riser/Limb Combos give you differant Bow length/draw weight, combinations. This was Bear Archery's way of allowing people to "custom order" the type of bow they wanted.
"A" Riser + #1 Limbs = 56" Bow
"A" Riser + #3 Limbs = 60" Bow
"B" Riser + #1 Limbs = 60" Bow
"B" Riser + #3 Limbs = 64" Bow
Most is personal preferance. Some folks like a longer bow, some a shorter bow. Some folks like longer limbs, for a smoother drawing bow. Some folks have a long draw length, and like a longer bow for less "finger pinch"... Like I said, mostly personal preferance. A new riser will probly set you back at LEAST $500, IF you can find one!!! I'd keep the riser you have, and buy extra limbs, IF needed. You were VERY LUCKY to recieve such a fine gift!!!!! You stated that it came with 55# limbs, and they are just about PERFECT as far as hunting weight goes. You bought a lighter set of limbs, and they will be fine for getting started on the "Traditional Road"... Looks like you're all set!!!!!
Good Luck!!! and keep us posted!!!!!