This post won't give your truck more horsepower, or get better fuel mileage. It just raises awareness of a question that was never asked. In other words this post is for those of us who like to document the minutest difference in parts for no apparent reason.

To wit: I have temporarily focused my attention on my '66 F250 to get it running because I've decided to scrap my '74 F250 due to extreme (for CA perspective) windshield/drip rail rust. There was a post on here about the sponge-like gasket between the 4-speed manual transmission and the transmission cover. The post also included a picture of a metal donut-type ring that apparently protected the sponge gasket. It was that donut-type ring that I wanted to access on my '66 F250 because my '65 F100 no longer had that piece. I must mention how I can't stand the pliable butyl rubber sealing compound used by Ford to seal the cover to the floor. I thought it was a fluke when I came across it in my '65 F100 but today I learned that the '66 F250 had the same vile compound as sealant. It is very time consuming to try to scrape that stuff off with a metal spatula.

While cleaning the underside of the '66 cover I noticed a lap seam across the cover. It looks factory made. Perhaps Ford had tons of one particular cover and through a design change decided to salvage what they could from the pile of extra covers. Additionally, the donut-like metal ring was not as shown in the other post but rather rectangular, as was the cover on this particular transmission cover. On the '65 F100 transmission cover, the opening is a circle with no screw holes to hold a rubber boot in place. I have looked at it closely for any sign of being a home made cut but it is clean with no telltale burs or other signs of backyard work. That is not to say it couldn't be done with careful work, but... failing any other explanation, I am now leaning towards a backyard modification.

At this time I'm reluctant to drill holes in the '65 cover to hold an old boot I found for the purpose. Were there boots available that merely seated within the hole like a grommet?

Have a look at the photos below.


The '66 transmission cover on the left, '65 on the right.Notice the absence of screw holes around the circular opening on the right.

Numbers stamped into the '66 cover

Numbers stamped into the '65 cover

Note the lap joint between the raised rib and square opening. The other cover is one piece; no lap joint.

Lap joint from the other side. 90 degree rotation

Original rubber boot with FOMOCO logo from the '66 with rectangular opening

Close-up of p/n from original boot

 

Might not hurt to get a copy of the MPCs. They are available for free download online. Part of what you are describing about the square opening and metal support plate for the foam is no mystery as you can see from this drawing from the MPC. Just a sample. You can see the representation of the butyl seal they used, too!