AMC manufactured this Typhoon (1960 G80TCS) with a steel gas tank using the following rear mounting bracket.
If you want an alloy or steel gas tank made in India, visit Vintage Motors Zone or EBay (larger selection).
http://www.vintagemotorszone.co.in/
If you want an alloy gas tank made in the United Kingdom, visit HoltWorks.
I ordered an alloy gas tank from HoltWorks with straight rear mounts. I will make my own rear brackets to fit different AMC frames. The delivery time for this gas tank will be about 24 weeks. I will use this alloy gas tank while the OEM Typhoon steel gas tank is being restored.