Couple issues on my new to me 65 dart…

Your carb is a Carter BBS. You can find a manual linked here. Search SlantSixDan's posts. RRR is right that search engine here is poor. I search FABO from google. I prefer BBS to the Holley 1920.

Your cowl rust-thru is near the left hole, so may be able to reach in to it. Also use the access in engine bay. I would leave a rag soaked in EvapoRust on it a few days, covered w/ plastic sheet. Wash and repeat w/ phosphoric acid (Concrete Etch at Home Depot). Prime then coner w fiberglass cloth or Bondo Glass. Keep the side drains clear and a screen or magnet cover to keep out leaves.