A couple of thoughts. Some states require a replacement motor to be equivilant to an emission motor offered for that year vehicle or newer.
You didn´t say which year your Grand is. Some of the transfers for the Grand are less than ideal and an upgrade or altenate may be worth some research.
Had a Grand with the 360 for 15 years, plenty of thump in the old motor, the TH-400 worked well and the axles held up (other than an occasional front axle U-joint). Pretty hardy truck, though I did break the transfer a few times and it did have a few electrical gremlins.