I owned one of these for three years, took it to the strip twice a year. JLT-II cold air kit and a Bamachips tune one it. Ran 13.40s @ 105.xx with it. 3.31s and a 5-speed manual, 30mpg on highway trips with the cruise on. Fantastic car.
I used the following oil in it:
Motorcraft 5w20 Synthetic Blend
Mobil 1 5w20
Mobil 1 5w30
Castrol Syntec 5w20
Castrol Syntec 0w30 (i.e., German Castrol)
Valvoline 5w20 (got oil change coupon for a gift)
Used Fram orange cans, Tough Guards, and Motorcraft Filters.
I can say with some degree of certainty, that the car seemed to run pretty much the same on everything. The best 1/4 mile time I got out of it however was with the 0w30 German Castrol, that is nearly a 40w oil.
Your friend got a fantastic car. Only complaints I had with it is the steering wheel doesn't telescope, and the seats kill your a55 after about 2.5 hours. Have your friend strap a Saleen twin-screw supercharger on it and really wake it up!