My under-car fuel tank is a 10 gal, ss tank, that I believe came with the car from SB. There shouldn't be a problem having one fabricated to fit your space requirements. Do you already have the window glass? My power windows came from "Specialty Power Windows" of Forsyth, GA. If you go online, you can view their products. They also make windshield wiper kits if you need it.
www.specialtypowerwindows.com