I've beat them in my ES with a 3.5HO, not sure about the differences to the 98 3.2 though.
As you already know, there's a huge performance difference between a not-even-close-to-stock 3.5HO and a bone-stock 3.2 that is 6+ years older and may have more mileage. Also the maintenance / condition of both cars factors into it.
I'd put my money on the Mustang. I think I'd be pretty dead-even with them in my '04 3.5 with Special PCM.
ROAD&TRACK April 2005 , test mustang V6 .
curb weight 3450.
0-1/4mile 15.1 / 92.7.mph
Of course that's with a "professional" driver I may be able to arrange a real world test tomorrow night on an 1/8th mile track between my '94 3.5 'Corde and my girlfriend's '06 V6 mustang.
Most intrepids can only do the 1/4 mile in the 15.5 to 16.5 range, depending on the little extras you put into the trep and how smoothly you get run it down the track. I've only "heard" of 3.5HO treps that supposedly do 15.5, but I have yet to actually see one myself. I also haven't seen a trep break 92mph at the traps -- this is Shadowvox kinda speed with his M.
If the V6 Mustang can get down there in 15.1 seconds, you might want to bargain for 2 car lengths!
Either way.....there's only 1 way to find out....get to the track and run what ya brung.