What's the best place to get some exhaust to make my stock 3 inch into straight pipe , or if I was going to buy a straight pipe where should I purchase 

 

If I remember right, the reason you wont see pyrometer thermocouples pre-turbo is because of potential failure of the thermocouple and being before the turbo.

Nonetheless, pre-turbo the highest "sustained" SAFE temperature is 1250*.  Common rule of thumb for most diesels.  Yes there is an approximate 300* difference when the thermocouple is post-turbo but the level of accuracy in that reading will be determined by location of the thermocouple.  So instead of 950* being the alternative temperature, its suggested not to run post-turbo EGT's higher than 900*.

Not laid up for several weeks yet but I'll see what I can find on that page about probe placement when I end up there.  I have couple other sources I can talk to since they are relatives.  One just retired from PACCAR but worked many years for Cummins and was shop foreman for a few years at Cummins/Swan Island, PDX.   Another one works for Freightliner and was shop foremen for a few years @ McCoy Freightliner/PDX.  Maybe can get some good input from those fellas.