Correction: All non-H.O. motors from '86-up are roller-cammed. Not all non-EFI motors were roller motors - pretty much everything from '85 back (excluding the 210-horse H.O. motor) used flat tappets. Just clarifying.
The Panther cars (Crown Vic/Grand Marquis/Town Car) did use E6 heads with flat-topped pistons, as well as a lame cam with a different firing order, a more restrictive upper intake, smaller TB and EGR spacer, and lower-output (14#, I think) injectors. All 302 Panther cars from '86 to '90 were speed density; in '91, the Town Car went with the early 4.6L, while the Crown Vic and Grand Marquis got one more year with the 302.