First, congrats, the Aero is a great machine.
Now, my '97 is a 3.0, which derives from the Brit engine family, while the 4.0 comes from the German side of the house, but I will tell you that my 3.0 is happy with anything you put in it.
I have 124K on the machine, and I change every 4K. It has seen years of M1 0W-30 (no longer available), several runs of RTS 0W-40 (a great oil, and still a decent buy at Wally World), as well as a number of runs of various brands of 10W-30 syns.
If I were suggesting an oil for extended drains, RTS 0W-40 would be a good choice, and so would the still available GC.
Good luck with your new acquisition. You should probably change the plugs and ignition wires, a really entertaining Saturday's worth of hard labor on an Aero.