12 bolts yes, not sure about the fan

Just to clarify are you saying all 327 cars got the 12 bolt or just that it was available as an option to any 327 car?

1965 was a bit funny. After only having the 10-bolt through 1964, for 1965 all 327 cars used a 12-bolt rear. Even a 250-horse 327 with a Powerglide would have come with a 12-bolt that year.

For 1966 there was a regression in that department, all 327s only came with the 10-bolt rear again (except the L-79 Acadians)

In 1967 it is generally thought that the 10-bolts were used on all Beamont & Chevelles through the 327 275-horse engines, but it is not commonly known that if you ordered a 4-speed with the 275-horse engine you got the 12-bolt 3.07 rear rather than the 3.08 10-bolt rear. That also held true in 1968.

1969 was something else different.

Steve, I can check the books to make sure but it is likely 3.36 ratio if it's a 10 bolt. Can you find the stamping on the passenger side axle tube just to confirm that? That two letter code would state whether it's a limited slip or not, what ratio and whether or not the car has metallic brakes. I'd be curious to see what it has. I have no doubts you are correct if your dad had it that long. I'm more curious to see the different ratios offered in the 4 speed cars.

I am not used to seeing 3.07 or 3.08 with 4 speed like Cameron says but I never say never!

Carl. Next time I go over I will check. Do you know if the stamping is on the top, side, bottom of the tube?

Regarding the  3.07  and 3.08  being used with  4 speeds;    the brochures say that the '65   327  (250 hp  and 300 hp)  4 speed  came with a 3.07
and the '66    283  and 327  4 speed came with the  3.08
I can vouch for the '66 beaumont 327  4 speed coming from the factory with a  3.08  as that was what was in my new '66  SD

I usually use 80 grit. It's stamped pretty hard so you won't be able to erase it very easily.

HI,A FRIEND OF MINE HAD A 65 BEAUMONT( ORDERED IT NEW) , 2 DOOR SEDAN, L-79 , 4 SPEED, 12 BOLT AND CLUTCH FAN. AND YES IT WAS FAST.

Yes  that would be kind of different.... an L79  in a 2 door sedan.  Might even be a bit lighter in weight than the 2 door hardtop that  the L79 was usually ordered in.  And  quite a bit llighter than a convertible with the L79.

Hey Carl;

Regarding the ratio's    you mentioned  i.e.  3.07 is a  12 bolt  and  3.08  is a 10 bolt 
Does that hold  for all GM  makes ?   Chev, Pontiac, Buick, etc...

Okay, if that is a fact; then there have been times when the factory build sheets  have not been  totally accurate.

For example:  I ordered up a 1970 Pontiac Lemans SW  with the 400  hi compresion 330 hp motor along with the TH400  and I asked for a heavy duty rear end.
The car came with a builsheet which said  GU4  3.08  and G80 positraction.

Quite normal looking  as 1970 Pontiac Lemans, GTO's and Firebirds usually came with 10 bolt rear ends....so the buildsheet seemed to confirm that.

I had that wagon for 8 years.  Along the way  in the mid 1970's  I took the car to a rear end shop to have it rebuilt.  They told me that they found something quite unusual for that model of car.  It had a 12 bolt heavy duty Chev  rear enSo  that would mean that the buildsheet did no match up with what was really  at the rear of that car.

After I see what you have to say about this example,  I have another example to share with you

Just scanning the parts page from the parts book. Hope it will be readable.