Ok, so my solidworks isn't playing the game, but here are some dimensions from my PDF's.
42L SWB carb/EFI vitara tank. ( same tank guard for both, so there is no such thing as a 50L SWB tank)
Bolt spacings.... Front flange ( closest to diff ) 455mm apart
Rear flange 480mm apart.
Tank body is approx 350 deep from front to back, and 700 from side to side.
55L 1.6 LWB efi tankBolt spacings.... Front 480mm
Rear 480mm
Tank body approx. 435 deep by 750 wide.
60L SV tankBolt spacing Front 480mm
Rear 480mm
Tank body approx 435x800.
From these dimensions, you can assume that the LWB efi and SV tanks will bolt to the same mounts. But you will need about 850-900mm between your chassis rails to get an SV tank in.
Hope this all makes sense

Thanks, that information is fantastic! Though it does confirm I will not fit an SV tank between the LJ rails
. Might have to go with the smaller tank...