Hello there mate,
Just finished going through your restoration thread, it is really good to see all the progress you have made. Wish I had half the energy to put into my projects as you have.
Regarding the "300 cu", I can't say I have ever seen that done. My first thought was the production date of your Skylark and if it was built along the same timeline as the Gran Sport. If so, that may have a bearing on the notation. There were some differences in the engine compartment between the Skylark and the GS. The battery is located on the right side in a Skylark, whereas the GS battery was on the left side. The horns are on the opposite sides of the battery. There are some other small details also. That said, the "300 cu" might have been done at the factory to help in assembly regarding those differences.
There are special plastic clips that go on the R/H inner fender to hold the battery positive cable in place on a Skylark. A GS does not have those clips because the battery is on the L/H side and the positive cable is routed along with the forward lighting harness. Two of the three battery tray brackets are also different between the Skylark and GS.
All that said and keeping in mind that the front clip was installed as one complete assembly at the factory, it kind of makes sense for the "300 cu" on the inner fender as a precaution to get the correct front end on the correct car. Just a thought on my part.
Loren
