Here's a picture of my 55 Buick. Can you tell what Series? A new frame is currently being manufactured and is supposed to be available next week. Still holding my breath and keeping fingers crossed. More information on this Buick can be found at http://www.adilop.com under the "Project" section. Why a new frame? To accomodate the disk brakes, air bags, new engine, etc! Great fun.
I'm guessing 50 series. The rear fins/decklid area looks like the super/roadmaster but with roadies being the rarest of the the bunch my money is on the 50.