I want to thank everyone that has responded. This is a great forum. I've owned this car since 1998 and never had issues with the FMX. It has a 351C 2V and I don't drive it hard. To answer the question about why and where I heard the FMX is too leak, this article
https://www.motortrend.com/how-to/0911rc-ford-automatic-transmission/ and my mechanic recommended I replace the FMX. That said, I've also seen similar posts that FMX can handle the power setup I'm planning. Based on these responses, I called my local tranny shop, and they agree they can build my existing FMX to handle this setup. They confirmed they can find the parts. With all of this information, I plan to keep the FMX and rebuild it. As mentioned previously, I do not plan to drive it hard - but, we'll see once I have 450hp at my disposal.
Right now she's getting suspension/brake make-over. Global West w/ QA1 front coilover, new sway bar, new rear leaf springs, QA1 rear shocks, Wilwood on all 4 corners, new 17" Legendary wheels. At some point, someone replaced the 3.00 to 1 locking differential with a 2.75 to 1 non-locking. I'm replacing and putting a 3.00 to 1 trac loc back. The engine will get a 408 stroker, aluminum heads and intake and a Holly Sniper EFI. In return, my wife gets a new kitchen make-over.