The saddle tanks work quite well. The manufacturer is "Tanks" in Minneapolis MN.
Some people have used a tank made to fit behind the rear seat. You'll need to construct a firewall between it and the interior compartment to insure your safety.
Another option is made by Rock Valley Antique Auto Parts in Stillman Valley, IL. This a tank that mounts under the body in the rear sort of like a Duece.
I love technology.
I am going to have to respectfully disagree with some of the other posts. I have those saddle tanks on my model A and they are a real problem at the gas station because the hose will not reach the far side of the car. You have to fill one tank, then turn the car around to fill up the other side. More trouble than its worth. I would go with a single tank design.
thanks guys. I tryed the saddle tanks [won't fit] so I went with the single tank behind the seat. I think it will work out. It is from a 78 Ford pickup. It stood behind the seat in the cab. I had to cut 22" out to fit my 29, it fills from the top. Thank for the replys