jim18655: Ya, that's what I'm thinking as well. I wouldn't understand why a perfectly good plate would have been bought for the purpose of simply raising the height of another, but if a junker was already in hand then why not.
I just measured the basement windows and you are of course right. The 24" dimension has tons of breathing room. Only pitfall is the excessive amount of snow entombing those windows at the moment...lol. Small hurdle really. Would be tougher clearing a path to the window. On the plus side the frost will keep the plate from sinking to the middle of the earth.
Your math regarding the overall weight worked out within a handful of pounds of mine.
Chiptosser: Still not completely sure if it truly is the way it was intended. The two separate name plates is enough to question it for me. All the other examples of Collins plates I looked at, although having a plinth of some fashion, none of them used a surface plate from a different manufacturer as one. Let alone a manufacturer from the other side of the country.