3900 lbs and manual trans will not be the issue. UNLESS its spends a lot of time on the drag strip

its when you pop a set of slicks on it and drop the hammer is when it will be testing the 8-3/4 's limits

for me personally it would come down to gear choices. And theres not much for the Dana in something street / hiway friendly
But with an OD trans and a set of 3.54';s may not be bad for longer drives