I will also reply In the 2stone thread below
to make it easier for someone else who may
have the same question.
I think I answered you by email, anyway
The Older Genesis are hit and miss. I have some reports
of them being very hot but mostly the main thing is the hood won't
close on some models with the 15" 2stone innside. This is not a problem for some
and others would rather that it closes. So most likely if you want to be 100%
sure the 13" will fit and with the grill skirt should do fine. If not, you always have
the option of upgrading to the oven since that is the same grill inside the oven casing.
As a rule though even the older Genesis grills tend to be on the hotter side than others.
Hope that helps.