are they gone...?

I was wondering the same thing... I saw that last time I went to his site, I think he still has some 40mm bottom ends but the engines all look to be 38 mm now.
I might need to snatch up a few bottom ends if that's the case, if he has any left...

Ive ran both the 38 and 40 MM bottom ends from dax and to tell the truth I liked the 38 balanced bottom end. as far as smoothness there both about the same but for the type of riding I do the 38 mm has a better placed power ban my 2 40s that I build do have just a little more top end going by gps but the 38 mm have a lower power ban which when in stop and go traffic it makes the 38 the better choice. all that said both are solid bottom ends.

The 2mm stroke difference shouldn't be too much of a power issue but they will have different port timings and the jug may need some shaving on the deck and/or base to put the timing where you want since it is enough of a difference to move where the powerband is at. Typically the 38mm bottom ends will have a touch more power in the low rpm range due to this slight timing change. This can be corrected for high rpm power or left alone for better low end power, or some more can be taken off the base for even more low end power.

Thanks Dave you explained it in a much better way then I did myself, and gave the reason for my experience