Thank you for your help.

[Copperhead]

I have a new to me 1966 Skylark Gran Sport. It has a 1967 400-4 engine in it. I need help determining what exactly the specs are for what is in it now.
I do have the protect o plate. I did climb under it and get the tag and casting numbers from the transmission.

Pretty sure it is a 1967 400 as it has the Star Wars air cleaner, distributor in front, and 400-4 sticker on valve cover. I did not get the engine number yet as I am fairly confident what this is.

Muncie 4 speed has tag 3734425 and casting 3885010
Pretty sure this is an M20 without having to take it out of the car but I would like help with the ratios

Rear end is a 10 bolt BOP but I can find no numbers

Here are all the protect o plate numbers excluding the original owners name and address
22-858
8-25-6 4N
6B146763

163 NN
446176B146763
MR519
G
NK177N
814

It's a beautiful car with restored interior and much restoration work already done, but it will obviously never be back to bone stock. We are trying to make everything sound and keep modifications tastefully "of the era"
Want to start by knowing what we have to work with.
Thank you so much for your help

 

[Copperhead]

 

[Copperhead]

 

[Dr. Frankenbuick]

The bolt pattern on the valve covers says Big Block Buick, but the valve covers dont seem right. There should be a flat spot for the decal. Check the back of the block where it meets the transmission. The displacement should be there.

Your POP supports that it is a 66 GS with a 400 Nailhead and an automatic ST300 trans. These had a 2.93 rear gear standard. Your current trans should have some letters and numbers stamped into it that identify it.

Your vin decodes as 446 = Buick Gran Sport, 17 = hardtop, 6 = 1966, B = Baltimore assembly plant, 146753 = number in the line for the year.

MR 519 = 1966 Buick Grand Sport 400 nailhead single 4bbl engine and date code.

NK 177N = ST 300 trans and date code.

163 NN may be the rear and date code. Check the 66 Manual to see the codes for the rear end ratios.

 

[Copperhead]

Thank you sir. Looks like I truly have a Frankenbuick myself lol.
I did share the Muncie numbers in the first post.
I will pull the cover on the differential and see if it has limited slip and identify the ring gear.
I will check the engine block number as well. Crazy that it went from automatic to 4-speed, wonder when these swaps occurred. If it could only talk.

 

[Copperhead]

Confirmed 400 block. Also I forgot to mention I changed the valve cover gaskets yesterday and the new Fel-Pros fit perfectly, I had ordered them blind for the 400....

 

[Dr. Frankenbuick]

Jack up the rear and see if both tires turn the same way when you turn one = posi. Count the drive shaft revolutions for one tire revolution for the rear ratio. Double the amount of driveshaft turns to one tire revolution if non posi or just count the number of driveshaft turns to two non posi tire revolutions.

I checked my 66 manual and OE is a standard 2.93 ratio rear and OX is a posi 2.93 ratio rear. The code is stamped on the housing, but it can be difficult to find or rusted.

 

[Copperhead]

Perfect. Thank you so much I was hoping someone had a simple solution.

 

[bob k. mando]

oh man, you got the Star Wars intake. sweet.