Came up on some Trannies....What fits my 90 Mustang 302 5.0??

either could fit or niether will fit. The C4 has a removeable bell housing, so if its not the small brock pattern you can swap to a SBF bell housing. The C6's came on SBF's and BBF's and do not have a removeable bell housing. The C4 is a better tranyn, and fits our cars. The C6 requires some firewall massageing to make it fit. The C4 also maintains a better HP output than the power eating C6.
 
I will definatly keep the c4 then.

And sell the C6 for some cash for a rebiuld kit and bell housing for the C4....(since it did not have a bell housing).........

I have a new AOD in my 90 but it's always good to have an extra tranny. I will rebiuld it with a shift kit and have it ready to install in my garage.