The core supports were the same but modified at the bottom much as you've done. On mine an inch or so of the lower vertical lip was bent toward the engine on each side to accommodate the longer cushions. As I recall my early 69 originally was screwed to the core support at the bottom. I don't know if mine was unique in that regard, but I think it was later that they started using a clip on each side that was an extended version of those used for the smaller radiators. I don't know if they are reproduced. Here are a couple of links.
Disregard those I mentioned in post 10 of this link. They are not the extended clips.
http://67-72chevytrucks.com/vboard/s...d.php?t=469356
Pictures
http://67-72chevytrucks.com/vboard/s...d.php?t=448040