Welcome to iRV2.
A couple of odd things here , first I can't think why a manual trans car would not be towable 4 down.
Any reason given in the owners manual , or does it just say no ?
Second, and I'll admit , I've never looked on the Remco site for info on a manual trans. I don't know why Remco would provide info on a manual trans car, yes or no, maybe because they used to sell drive shaft disconnects.
Have you tried phoning Ford or Remco , for more info?