Remove all spark plugs and test each cylinder with a proper gauge . Determine if any damage was done , check engine's health . Sounds like you got lucky , 4.0's are tough . Still , this is something I would recommend before any engine work . Circles the problem area if any .
You can also just take the cap off once re-filled and check for bubbles constantly coming coming from the coolant . In this case , just re-fill it with water and call it a flush of sorts for testing purposes . I think it would bubble through the coolant reservoir also when at full operating temp