I replaced all the lines on a 55 3600 about 6 years ago and used the Copper-Nickel with standard fittings. It is still working great with no problems. I don't recall it being an issue at the time. If I remember correctly the vendor that provided the line also furnished the fittings.
Fred

1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine