Barb, the Caddy had a quadrajet on it originally and that one has a different bore pattern than Edelbrock or Holley square bores. Adapter plates are available and Edelbrock (and maybe Holley) make carbs with the q jet pattern, but they are pricey.

Cheapest alternative is to put another q jet on it. Some people love em, some hate em, and I personally have no problem with them. They have been used on a ton of factory cars over the years and almost every marine v8 engine is running one (until efi came on the scene). If you decide to go that route you can find them in junkyards (get one without all the vacuum ports and emissions stuff), or, there is a company in Jacksonville Florida that sells rebuilt one outright on Ebay for about $ 200.00. My Son Don just ordered one for his boat and it was about half price over what Summit and others get for theirs.


You can even use one from like a 454 boat engine, they are identical to car versions but have a different vent tube to prevent explosions in an enclosed bilge area, but in a car they work the same.
Don