Hello.
This was my fist build. It took forever, it required a lot of fabrications and modifications... And finally...
I put 56 tooth sprocket for torque and a spring loaded tensioner. Surprisingly, this thing is working. It goes about 18 MPH. I'm on my 4th mile and still alive.
I found it on Ebay. Look up seller named myersfab. He can make a tank with your specs at a reasonable price. His name is Tony and he is nice to deal with.