I wasn't aware it could be modified to make it a 19 gallon tank... Honestly, I thought I had a 15 gallon tank
Well, @tr21triton says that the 4.0 has a 19 gallon tank, but since it's a 97 one never knows. The mod is very simple, and involves trimming back the vent tube on the inside of the tank. I wrote about it, with links to where I learned it, here.