Hi All & Merry Christmas! Is there anything on the Ident plate on firewall or other source on vehicle to know what rear differential came with it?

Sadly no, it is not part of the VIN or ID plate. You can get that information from the list of option RPO codes either from your Pontiac Historic Service documentation, your original MSRP sticker, or the list of RPO codes that should be on the inside of the glove box or driver door for later model cars. With that list we can translate the three letter RPO codes down into actual options. Most axle RPO codes begin with the letter "G".

This is an example of what you are looking for in a late model GM vehicle:

Assuming this is a 3rd Gen Camaro example, GU5 means a 3.23 rear axle. Since G80 is also there, this means this car came with a POSI rear end. Without G80, it's an open diff.

Edited December 27, 20214 yr by Frosty

Since we are talking about a '67 GTO, then we need the build sheet (under the rear seat or sometimes there is a copy on top of the original gas tank if they are unmolested cars and the mice, water, dirt, grim or time haven't destroyed them), or the PHS documentation.

Here is a list of all the optional rear ends for a 1967 GTO

Thx, unfortunately nothing was under rear seat nor above gas tank. 
I’ll check D-door for RPO Codes. Is it a sticker in glove box? 

SInce we are talking about a '67 GTO, if the original build sheet isn't under the rear seat or on top of the gas tank (between the gas tank and the body and you don't have the original MSRP sticker), then you need to order a copy of your car's paperwork from Pontiac Historical Services.  Give them your car's VIN # and your credit card. They will send you the build sheet and a reproduction MSRP window sticker. All valuable information to have. Money well spent in my opinion. This will give all the RPO codes / options your car left the factory with.

http://www.phs-online.com/

Thx Frosty

Your welcome. More modern cars - such as 3rd gen Firebirds had an RPO sticker put on the inside of the glove box. Sadly this was not the case of the sixties and seventies cars, hence the need for the PHS documentation. Luckily for us, Pontiac (PHS specifically) is one of the few GM marks that you can get this information.

Most of the rest of GM's divisions lost this information over the decades. So if you own (say) a '69 big block Corvette - unless you have the original build sheet or MSRP for that car that came with it, Chevrolet can not validate anything except what is on the VIN or the data plate on the firewall.

Edited January 18, 20224 yr by Frosty

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