I've posted in my build thread, but I'm also running a TM38 modified by HPR to a 41mm.  I'm running a main jet of 660 the last time I was in the dunes. It was just a little rich, so I figure a 640 should be good for Glamis and the temps between 70-90.

I'm heading out again for Thanksgiving, so figure it will be colder out there, so my 660 should be fine for the colder temps.