I used metric extenders to lengthen the studs.
Threaded Standoff's will work, basically they are just just 1"-1.5" long nuts.
Screw one on each tank stud half way, then run 4 new bolts up from the bracket into the other end. You can hold the stand-off nut with a wrench to tighten, and use lock-tight!
As for tank padding I use the scrap from the BMX foam grips I put on all my builds, just 1.5" long cut in half long ways of the grips diameter right where the studs go down. They disappear from view but give you a 3/8th" weatherproof foam cushion.
Or better yet, save the pretty top bar of the Stingray and pitch that butt ugly 1/2 gallon tank and put on a $125 seat mount 2/3 gallon tank like I did on this Caddy so as not to goob up it's pretty top bar.
BlowByU sells a tank for $320+
I had Coyote Tanks make mine for $100 delivered, and I used 2 of plates from the pile of 3 hole 'rag-joint' spare plates to hook it to the seat bolts.
My point is you are building a Stingray, a tough job in itself, so think outside the box when it comes to where and how to store the fuel is all ;-}