I was rain racing around and spun the tires at a stop sign with a slight incline. It spun 3 times and i let of i heard a shutter sound after this was all under 25. i pulled in to my driveway and put it in park. when i try to back it up again no go it goes in a forward gear in reverse and never rolls back even in neutral. i removed the drive line to back it out. this brings me to my question i was thinking of changing out the transmission with one from a 1981 v8 318 car would the flex plate from the 6 bolt up to the 318 transmission i believe there both 904,s or should i just rebuild the semi operational 6 transmission?

The flexplate isn't the issue, the bellhousing won't fit.
Sounds like the old "sprag frag" to me, close the throttle with the tires spinning and it blows the rear sprag. If you can do trannies, go ahead and swap the guts, hoping it didn't chew the case inside. Otherwise, /6 trannies are easy to find.

_________________
O==\=/==O

"A mechanic is Somebody."
- Jim Preston