These Units are Similar in Appearance, Although the 290-212 Has a Thicker Aluminum Rear Mounting, While the 290-212A and B Have a Thinner Steel Mount. Both Interchange. All 14684's Have the Same Plug Configuration ("D-IG-L"), Although Regulator Numbers Vary as the Size of the Regulator Varies. The Same Unit, But With a "C-IG-L" Plug Is the 14937 (OEM No.100211 4150). These Units All Use a Single V-Groove Pulley. Later Models (13214) Used a Serpentine Pulley. The Pulleys Will NOT INTERCHANGE.