I believe you may have a Carter Thermoquad carb. These carbs were put on all SD455 Pontiacs. They were used on a lot of the large cars(Gran Ville and Bonneville) and they are a bear to rebuild. If you think a Q-Jet is tough, open up one of these jewels. However, they are very good carbs if rebuilt properly. Here's a good site-http://www.offroadexchange.com/projects/CrtRbld.htm. Get a new set of points and a condenser. Coils will usually fire okay until they get hot from running for a while.
