I think there are a lot of adventure-type movies that would be better suited to a 6 and 8 year old than the Indiana Jones movies. My boys are 4 and 5 and would love to watch them (for some reason those movies are marketed on kids’ channels and kids’ cereal boxes). I wouldn’t let my kids watch them for many of the scenes listed above.
Faces melting, fist-fights, the guy who gets chopped up by the airplain blades, shootings, the guy who drinks from the wrong chalice and turns to a dusty skeleton…it’s been a while since I’ve watched any of them, but those are some that come to mind. I believe there are some sexual references in some of them—don’t Indy and his father have a thing going with that blonde? That might go right over the boys’ heads though.
I’d suggest you watch them, as others have mentioned. You know your kids best, if they won’t be bothered by those scenes, you aren’t bothered by your boys watching those scenes, or you think you can skip parts, it’s your call. My boys did recently watch parts of Jurassic Park and loved it.