It is very easy to find quick references for the various doneness temperatures (rare, med. rare, etc.) of different animal meats, but not so easy when it comes to offal. Sweetbreads, as far as I know, are usually prepared by poaching or blanching first, then a resting period, and then a final preparation like pan-frying before being served.
So, at what temperature are sweetbreads "done" (the temperature they should be cooked to during poaching/blanching)? Or is there a range (rare to well done)? I've never been served sweetbreads at a restaurant and had them described as being at a particular doneness, so I'm guessing there is one small temperature range at which they're not dangerous, and not overcooked. Most recipes I found just give a period of time for which they should be cooked, which varied greatly. The few references I found online which mention temperature at all only mentioned the temperature of the water bath for cooking them sous-vide (usually between 150-160 F). That seems a decent guideline for doneness, since cooked sous-vide, the meat will end up at the same temperature as the water. But never having cooked them, I can't say for sure…
Best Answer
While not perhaps a definitive answer, according to Serious Eats:
This implies that sous-vide is perhaps not as helpful for sweetbreads as it might be for some other foods that are more temperature sensitive.
The only recipe I could find that mentioned a temperature was a sous-vide based recipe that suggested 60 C (140 F) for one hour. Note that this is one of the time and temperature combinations that essentially kills all pathogens that may be present.
From these facts, I infer that you want them cooked though (which the traditional blanching method will ensure), and hot for service, but a specific temperature as is used for beef is not important.