First let's clarify that the original post is about whether it is a model 9487 Toronado or a 9687 Toronado Custom. *Not* whether or not it was a GT, which was option W-34 available on either model. 23,082 1970 Toronados were the Custom and 2,351 were standard.
Yes, there is something that happened with the model numbers in 1970, but I can't find the info on it yet.
I had a mostly original W-34 a few years ago. Original paint, etc. Was a truly impressive car to have. Unfortunately, after I sold it, well, take a look for yourself:
http://wmachines.shubes.net/OldsWMachinesPast.html