18 or 18.5 is about it for a fan size in a factory shroud. Stock dirrect drive fans are plentiful and easy to come by. They just use a little bit more power to run is all. Your best cooling will always be with a fan shroud, the right size fan and set in the shroud the propper depth. A jag clutch is some useful info to jot down. If you ever go that way. Neil gave you some school of hard nox info there. A 19 inch fan does not fit an E body shroud either, not without mods anyways