Adding to the thread after 15 year gap
Yes I was curious and found this thread with the awesome picture on top as well.
In addition to the cartridge differences, I have Armor Battle boxed with the 'heavy' shielded version. There is another minor difference in that the top of the box has a computer number printed direclty on the box itself. All other INTV boxes either don't have the number or have the number printed on a white label which is affixed to the box. I can supply a picture if anyone wants it.

But yes - the shielded INTV carts are much heavier - easy to notice. And they seem very rare as I've only ever seen a few.