I had no issues with the water temp, fit right into the manifold. The
oil temp fitting supplied was a BSPP(British standard parallel pipe) by 5/8-18 as you said. I didn't want to weld this fitting to the pan, and was unable to find a sealed bulkhead style fitting for the BSPP to screw into. I took a 5/8-18 bolt and drilled a 1/2 inch hole through it. Used teflon washers to seal on the pan, and inserted the probe through the bolt. Worked well.
Dave