Nope, the one from the FMX does not fit!
Here's what I used and it was a perfect fit and very sturdy at that!
https://transmissioncenter.net/shop/crossmember-1967-to-1973-mustang-with-aod-transmission/
Yes you can but I wonder if you should.
Mine has a flat hood too and I’ve had a round hole cut out above the filter so the air can actually enter through the 1969 Mach1 hood scoop I put on the hood.
That of course meant cutting the brace and it held up nicely but every time I look at it I feel...