According to Dave Kessler, whose shop was an authorized B&S dealer,
the Series 2001 and Medusa were pretty much the identical horns.
This is how he described them on the Kessler & Sons website:
The B&S Series 2001 is the predecessor to the Medusa.
For the tenor sax, the body tube is the identical design to the Medusa.
There are only a few minor differences in key design.
Here are the few differences we have been able to identify:
Series 2001: Low C/D# Cluster 2 Separate Rods. Medusa (Series 2006): 1 Split Rod Mechanism.
Series 2001: LH C#-B Rollers are 2 Separate Rollers. Medusa (Series 2006) 1 Roller; 1 Tilting Connector Roller.