It IS a Curio & Relic Firearm (technically) and no, you do not need a C&R FFL to buy one.
Curio & Relic Firearm is defined in US Law as a firearm that is 50 years old, or older, OR is on a list of firearms published by the BATFE. (All Colt Woodsman pistols, ALL Winchester Mdl 88s, regardless of age, etc) So a Marlin 39A rifle that is 60 yrs old is a C&R- one that is 49 years old is not.
The 03 C&R FFL permits the holder to acquire and dispose of C&R Firearms across a state line without going thru a dealer. I am in VA, find an M1 Carbine in Idaho that I like, seller and I agree on a price, I send him a signed copy of my license, he puts carbine in the mail to me.
HOWEVER- you, one of the unlicensed masses, may go to a dealer, fill out a form 4473, get a background check, pay the man, and pickup your M-N 91/30. I just have a lot less paperwork to do than you do.