Technically the driver side mount tower on a slant 6 k frame is the same as v8 so you could cut off the old pass tower, drop a empty block & trans in bolting it to the drivers and trans mount, then with a floorjack underneath use a level at the front end of the valley using the floorjack under the motor to raise or lower the pass side to spec/level.
Weld on a pass side tower and you're set.