You'll get other responses but let's first state that the dpi you're associating with the images has no meaning. dpi only counts on the paper. so, you need 8x10 aspect ratio. you'll have to crop. it's better you crop than just allow the print process to pick whatever it wants (maybe the middle, maybe the side, maybe it'll stretch-to-fit).
presuming you'll print the first one with the 10 inches being the long side, the 8 side should be cropped to 3800 pixels. the print software will then have the approx correct aspect ratio and will resize as it likes. ok? (i'm leaving out as i don't understand it too well the idea that maybe dimensions should be on16 bit boundaries. i doubt if it matters if a few pixels get tossed away).