To Use or Not to Use 3D Physics in 2D Game

I have a lot of scripts written for a 3D game that would be useful in a 2D game, and I really don't want to reinvent the wheel to add them to that game. So my question is, can I use my current 3D game scripts (with Vector3s and calls to Physics.Raycast(), Physics.Gravity, etc.) in a 2D game (where all the GameObjects have 2D components like Collider2D and Rigidbody2D and there will be other scripts using calls to Physics2D.Raycast(), Physics2D.Gravity, etc.)? I'm guessing that I can do it but that it will be stupid inefficient, so I might as well re-implement with 2D classes, but figured I'd ask first.

Thanks in advance!