here is a picture of my original rzv500r tank .
( It has been epoxy coated inside , so that is why the metal sheet look thicker than normal ...)
I agree with Giron , you should at least try to find the original sender unit , the right handle switch and the temperature/fuel combination gauge .
auction.yahoo.co.jp is your friend ....
Do not hack you original wiring harness (This would be pity ) just buy the connectors needed and build/add a small additionnal wiring harness with the additional
wires for sender/gauge/switch etc .
Fz750 gauge is also an option , if you do not mind not being strictly original .
https://i.ebayimg.com/images/g/8UwAAOSw ... s-l640.jpg
modifying an rd500/rz500 tank is also an option but , it is a a bit delicate , and there is a non zero risk of permanently damaging your tank
if the modification is botched .... also you should be very careful about making it leak-proof .
As you probably well know , welding a tank without degassing is very dangerous ..
I did the same modification on an Rg500 tank . ( i did not do any welding , holes were drilled in the tank bottom ,then nuts were sunk in epoxy on the inside of the tank ...)
The Rg400/500 (JDM) have a recovery cup with a a drain tube under the sender unit in case of leak (much safer ).
the RZV does not have a recovery cup ...