https://www.importavehicle.info/2017/09/toyota-supra-buyers-guide-jdm-vs-usdm.html
There’s a table on this web page, which gives you the build numbers by year.
VVT-I was introduced as per the table, so your build number will need to be equal to or after that displayed for vvt-i.
Late models lost the E designation, and gained GF at the start designating frame number.
This is displayed right at the start of the numbering system.
Obviously, as mentioned you would want to see an ‘F’ for a 6 speed in the number.
Another set of code detail for drive train can be seen here.
http://www.toyota-supra.info/forums/mkiv-supra/14011-vin-number.html
Ultimately, 6 speed will be v160 (non vvt-i) or v161 (vvt-i).
Hope that helps