Personally I would have a hard time dumping conversion money into a 80 that old. Even though you will never be able to recoup your investment a newer model with lockers would make more economical sense.
Having driven a 4BT you could not give one for free due to vibs/noise - sorry 4BT guys. 6BT is in a whole different class.
If money is not a concern a LS3 with a 6speed would be a great choice with a ~4.0 1st gear
What he said ....