rear pinion seal info needed...

Hi. Jeff here - a new guy, based in Boston, MA, in the Fenway - the very heart of Red Sox Nation! I have a question for the forum:

I have a leak in my rear pinion seal. The car in question is a 1968 Mustang convertible, (my third one...) with a 200 cubic inch straight 6 engine. The VIN is 8T03T205597, if that helps. I need to know what size I need to get in order to replace it. My mechanic tells me that there are 3 possible sizes, measured in inches, relative to the ring gear size.

Any info from the forum members would be much appreciated!
You can post here, or Email me directly: [email protected]

Thanks in advance. :wavey

Jeff in Boston