4-speed o/d swap

I have a 74 dart sport that I bought new with a 318 and 3 speed on the floor. Many years ago I put a 4-speed in it with no problems. Now I am looking at putting in a 4-speed O/D unit in it. I have the proper 318 (O/D) bellhousing and O/D trans unit.

Question is are these bellhousing the same size as my stock one and will my existing flywheel fit this bellhousing and engage the starter properly? Anything else that I may need to be aware of?

Thanks in advance.

Dart Sport