[rotorwrench]

The half bell case was used from the beginning of the 1949 model year up to sometime in the early part of 1951 for Mercury cars. It was likely around February of 1951 or there abouts.

The Lincoln case may work but make sure there wasn't some difference between the late V12 bolt up and the smaller Ford/Mercury little brother. There are variations in the way the OD tail housing was made in some years. The gears in the transmission housing should be interchangeable even though Lincoln had close ratio gearing. The internal lock out control for reverse is important too. It will have to match the Mercury housing.

A corroded case may be OK but it depends on where all it is corroded. The problem areas are the same as for the older Ford & Mercury cases. Cracks around the front counter shaft bore and extreme wear on the rear thrust surface of the counter shaft. If it has bad flange pitting then a person can use Devcon plastic steel to level it back out as long as there is still a flange to work with.