I ran into a problem with my 340 and stock exhaust manifolds running hot. Put headers back on it was fine. Suggestion did you use a 8 blade pump? If not get one they will generally run the engine cooler. I currently run 190-195 in this 90degree heat nothing ar=t all with that when running a 190 stat. Suggestion also a heavy duty declutching drive fanfrom a dodge pickup will also help but if stuck with need for short shaft unit use one that will give you best idle cooling using a thermo spring on the drive