Good luck trying to find one of the original RS option big side tanks in the UK... They go for big money (RS option only originally and quite rare then) and a quite rare now from what I have seen / read...
Never seen 1 for sale in Aus in 20 years and only seen 1 in the flesh in Aus...
All Mk2 2Lts used the Aussie drop tank under the boot floor, and so did the later 1.6Lt cars... Only the very early Mk2's in 1.3 and 1.6lt for used the side tank. If you are looking for a side tank to use with a 2Lt - try to find the sender unit from an early M2 1.6Ghia - as they have the return line into the tank for the Weber 32/36 (in addition to the fuel out). Almost all others have only the fuel out line for the VV carby. You can just block off the return line at the carby, but it does put a little extra stress on the needle n seat in the float chamber (but it does work OK)...