They are directional. Most serpentine systems on V8's are reverse flow from standard V belt fans.
The good news is. Most Inline 6 water pumps can reverse and still pump just fine. You need to look at the water pump vanes and see if they are curved or straight. Curved = directional.
I see no reason the 3 blade will not work. You make a good shroud and try it. You may have to buy a 5 blade later. That 3 blade was used on 305 V8 and possibly 350's.
I run a 190 stat in my stuff. Goal is to get the temp up fast to get a normal size on pistons/ block soon as possible. This slows wear. Also keeps the engine cleaner by getting the oil hot enough to evaporate any condensation that gets into it from the heat/ cool process.
