the track is only as strong as the sides of the truck at the hight they are attached, so no absolutely not suitable for machine tie downs.
the truck maxes out at 7K, but that's a distributed load, and also obviously that has nothing to do with the E tracks rating.
I like the idea of welding rings on, but ive screwed D rings to rental truck beds for tie downs (shhh, don't tell them!).
never for anything as heavy as 3k though. If you use a decent deck screw or such, like the SPAX screws, and use
enough of them and numerous tie downs like 4 font and back with 5 spax screws each in line with the load, id call that
ok for a BP type on short runs. don't secure the straps higher than the top of the knee cranked all the way down of corse.
that would just rip out the screws.
last time I moved a Bridgeport style mill, it was in a box truck and I secured it thusly.
I had removed the head, ram, and table though. I had to, to get it out of the previous location, through a 1/2 hight door.
(why they would have put in a hobbit door I have no idea...
)
in short, I would highly recommend taking it apart to reduce the center of gravity hight and distribute the load, if at all possible.
good luck! drive safe.