Does anyone know for sure if a plastic tank will work on a 620? I heard somewhere that it would not work and I can't remember where or what the reason was. Seems like it was something to do with the fuel pump.....
This is from an ebay listing by proItalia:
This set is a fairing kit for your Ducati Monster. This set comes in glossy black with a white stripe and includes a fuel tank, windscreen, seat cover and front mudguard. This kit fits many** different Monsters that have a plastic tank. Should you wish to confirm that this part fits your motorcycle, the official Ducati part number for this item is 96970604B. Retail is $1650.00.
**READ CAREFULLY** THIS KIT FITS THE FOLLOWING MODELS
2002 Monster 620
2003 Monster 620/800/1000
2004 Monster 620/800/1000
2005 Monster 620/S2R800/1000/1000S
2006 Monster 620/S2R800/S2R1000/S4RS
2007 Monster 695/S2R800/S2R1000/S4RS
2008 Monster 695/S2R1000/S4RS
So ProItalia's listing seems to confirm that a plastic tank should fit a 620.