I looked at the SS Brewtech web site, and the port is not a threaded 7/8" fitting, just a 7/8" through hole, and they sell parts to fit in there. The bulkhead fitting to 1/2" NPT (FPT) is listed as fitting into a 13/16" hole. With that in place you have a whole lot of options for thermometers and thermowells.
--GF