Robbie,
Here are 1961 Chevrolet factory Rear Axle codes and ratios:
I believe the 3.55 ended in 1960 and replaced by the 3.38 in 1961.
Series Code Ratio Plant
Corvair 95 BL 3.89:1 Detroit Gear & Axle
Corvair 95 BY 3.89:1 Detroit Gear & Axle
1/2-Ton MA 3.90:1 Detroit Gear & Axle
1/2-Ton MB 3.38:1 Detroit Gear & Axle
1/2-Ton MC 3.90:1 Detroit Gear & Axle
1/2-Ton MD 3.90:1 Detroit Gear & Axle
1/2-Ton ME 3.38:1 Detroit Gear & Axle
1/2-Ton MF 3.90:1 Detroit Gear & Axle
1/2-Ton MG 3.90:1 Detroit Gear & Axle
3/4-Ton MH 4.57:1 Detroit Gear & Axle
3/4-Ton MJ 4.57:1 Detroit Gear & Axle
3/4-Ton MK 4.57:1 Detroit Gear & Axle
1-Ton PA 5.14:1 Detroit Gear & Axle
1-Ton PB 5.14:1 Detroit Gear & Axle
Just thought I'd add some info.
Brian
