<font color=purple>Basically, he'd be switching from 35's to 33's. Assuming he has an automatic with overdrive, that wouldn't be too bad. Running in O/D, 4.56's have the effect of running 3.19's (again, assuming the automatic as O/D isn't as drastic with the 5-speed). Since the "highway" gears in the pre-overdrive days were 3.08's & those would come with 31's stock, no big deal. If he has a 5-speed, or no overdrive, 4.56's may be a bit much for 285/75's.
To do some math, let's assume that his 35's really are 35" & that his replacement 285's are a true 33". And let's assume the TH700 automatic with a .70 overdrive 4th gear. At 60 MPH with the 35's:
4.56*.70*60*336/35 = 1,838 RPM's
With the 285's:
4.56*.70*60*336/33 = 1,950 RPM's.
Not a big difference & certainly not high RPM's in either case. Assuming NO overdrive:
4.56*60*336/35 = 2,626 RPM's with 35's
4.56*60*336/33 = 2,785 RPM's with 285's.
In this case, he's already pushing it with the 35's & I wouldn't want to drop down in tire size.
Is this any help?</font color=purple>