The common problem is the syncro but as mentioned above a 50 year old vehicle can have other worn parts. You can get a rebuilt 2-3 syncro assy from Anaheim Gear in Anaheim, CA. for $125.
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