C4 is a pretty bullet proof trans. depending on how it is build. Sounds like you are really just wanting to swap to a manual regardless. You really don't want the original Manual trans for a Maverick as they were all 3 speed top loaders and not that great. A regular ole T5 like the fox body Mustangs ran/run will handle quite a bit of punishment but if you are running enough HP to cause problems with a C4 then you will likely want to have the T5 rebuilt with some upgraded internals.
A good 4 speed toploader would be, and has been my choice for a manual trans in my 73 Maverick. Shopped on Ebay for mine and took my time and got it for less than $1000 shipped to my door, completely rebuilt from ground up. It was built to be put behind a 390 mustang so I just had the guy that I bought it from changed the input shaft to fit my 302 applicaiton and I had to find the correct bellhousing.
I have put it through some pretty harsh driving on the street and the track and it is solid as a rock.
Just be careful if you go with the 4 speed and make sure it is a real toploader and not what they call a toploader imposter. Those are basically a 4 speed that looks similar to a toploader but internally it is actually a 3 speed with 4th gear being OverDrive. There is actually a bulge in the case that you can look for to accomodate the larger 4th gear.
All the info you need is on David Kee's toploader website
David Kee Toploader Transmissions, Inc.
