I had a minute so I machined an adapter to get the 11.5mm AR5 shaft to work with the stock rubber isolated Miata shifter. I just turned down the shaft to about .002" bigger than a hole I bored in the adapter, heated up the adapter, froze the shifter and pushed the two together real quick. There's only about .260" of shifter shaft in that adapter, but according to my first failed attempt at the heated press fit, it's damn near impossible to separate the two.