Yes, the crossmember is the same from 3.8 to 5.0. There are actually 2 different crossmembers, one for 89-92, and the other for 93-97. The only difference is that the later one has the motor mount pads 1” further apart. As for a tubular K-member, AJE did make one, but it was expensive and required their LCA’s as well, and many people who had them said they were not good for a street car.
As for a Cleveland swap, I think one was done a while ago. It should physically bolt in the same as a 302 or 351W, so if you get mounts from a 5.0 bird, it should bolt in, and either the AOD or the M5R2 will bolt up to it. I think your biggest issue is going to be headers, since our engine bays are not as spacious as a Mustang’s, so you may have to try a few different ones, and maybe even modify whichever ones hit in the fewest places. Also I’m not aware of any EFI intake manifold for the Cleveland (though it has been many years since I looked, so they could exist now) and a carb swap into a car that came with EFI is just hacky as far as I am concerned.