Just to let you know, my balancer has all the details Bob mentioned: Beveled edges front and rear and timing marks. The 427 damper simply has a single V groove on the back edge of the pulley groove, as the timing marks are on the pointer on a 427.
I also noted the drilled holes on your damper are different than my C6AE Re-stamp. Many early dampers are spot faced off with the stamped 6. I have my engine out currently and will try to take a picture and post. I would try media blasting your pulley as Bob suggested to find the timing marks. If they aren't there, you have a 427 damper.
There is one on Ebay currently. However, 1000.00 is a bit pricey.
-Keith