can anyone tell me i f a v8 auto will bolt up to 6cyl engine?

what box is it, & why would you want to?
in the manual single rail, the 302 & 250 6 cyl had lower gearing and the 351 had a taller 1st gear, I believe the C4 only requires a bellhousing swap but don't quote me on that. As for the FMX , I don't think they were ever fitted to a 6, so a belhousing may be hard to get. you can get an AOD 4 speed auto for peanuts now, but you will have to get an aftermarket belllhousing.