The 4L80E has the same output spline as did the turbo hydra-magic 400. Your old bolt on yoke should slip into the output but may not have a drilled and taped output shaft for the retaining bolt. I have hand drilled and taped these before. They don’t have to be perfect to hold a yoke in place. Your other choice to use the original driveline is swap output shafts from old trany. Not great idea as it’s the last part out in tear down. I assume you just installed a used transmission that is the same model and length?? Good luck.