Here's what you need to consider when finding a replacement:
* Bellhousing Bolt Pattern: The most crucial factor. You need a transmission with a bellhousing that matches the bolt pattern of your 223 I6 engine. This is usually a specific number and arrangement of bolts. Incorrect bolt patterns will prevent the transmission from mounting to the engine.
* Input Shaft Length: The input shaft of the transmission needs to be the correct length to properly engage the clutch.
* Transmission Case Length: The overall length of the transmission case needs to be compatible with your F100's frame and drivetrain.
* Year Compatibility: While other Ford transmissions *might* fit, sticking with transmissions from similar-era Ford trucks (late 50s and early 60s) dramatically increases your chances of success.
Finding the Right Transmission:
1. Identify your original transmission: If you can still identify the transmission code on your truck, this will help you find an identical replacement.
2. Consult a Ford parts catalog: A parts catalog specific to your truck's year and engine will list compatible transmissions.
3. Check with transmission specialists: A reputable transmission shop can help you identify compatible transmissions and potentially source one.
4. Online forums: Searching online forums dedicated to classic Ford trucks can yield valuable information from other owners who've tackled similar projects.
In short, while a 3-speed manual is the most likely original and easiest swap, you must verify the bellhousing bolt pattern and other dimensions before purchasing any used transmission to ensure a proper fit. Don't assume compatibility.
