[84LX89GT]

Here's what i would try without knowing much about what you've done so far:
cycle the key a few times without cranking. locate the schrader valve on the fuel rail and push in the plunger in the center with a pointy object and see if there is actually fuel there. If not you might have a bad fuel pump, plugged fuel filter, bad fuel pump relay or other fuel related issue (something stuck in fuel pickup - sugar in the gas tank).

Find the pcm power relay and swap it with a relay you know works like the blower motor relay or something along those lines and see if it starts up.

get some insulated gloves and if possible spark plug wire pullers and hold a spark plug wire just off about 1/4" from where it plugs onto and see if while someone else cranks there actually is spark there.

Also pull the spout connector and check timing while cranking and see if the marks jump around (timing chain jumped), also do a compression test, if compression is low (should probably be 140 psi or higher) then it might be a jumped timing chain (i've had two mustangs that have had that happen). I don't know how many miles your mustang has, but 150,000 miles seems to be the magic number for timing chains going out, at least for me.

Keep us posted.