all 260, 289, 302, 351 based small blocks will accept the stock bell from a v-8 4-speed mustang II. keep in mind the v-8 4-speed bell is specific to mustang II.
there may be others that can be massaged but i am not aware of one. the t-5 bell would be an option only if you were going to a 5 speed.
someone can chime in to confirm but i believe the v-6 4-speed bell has a different bolt pattern.
Do you have a v-8 rad transmission? I'm guessing since you said its out of a 75 that it is not. In any case the v-8 and 4/6 transmissions used a different input shaft and different gear ratios. The ratios would not stop you from using but the input shaft will.