Several ways to do it. You can jump thru all the hoops the DMV will throw at you and get new title, you can buy an old title "Historical document" on ebay from another vehicle or at a swap meet, buy some vin plates from someone like Speedway Motors, stamp your numbers on them and rivit it to your frame, and a couple other ways. my 26 Fod is registered as a 1918 using an old title and I got the number stamped and rivited on the frame. most rat rods just buy the old title. My friend just bought one for his 49 chevy fo $200 but I've seen them go as low as $50. more info here:
Title talk - KillBillet.com "The Rat Rod Forum Dedicated to fun, low budget, traditional, rusty, patina Rat Rods and Old School Hot Rods built with junk yard parts."