I wouldn't worry about it being from a V6.
I believe it may only have one less friction and steel plate in the 3-4 clutch pack.
The 283 probably doesn't have a whole lot more torque than the 4.3.
The same torque converter is OK, but I don't know if the 283 has a smaller flexplate and different starter than the 4.3.
If so , use the 283 flexplate.

Your tranny is a 1986 unit BTW.