1986 lincoln hearse rear coil springs

I have a 1986 Lincoln town car hearse that the previous owner must have heated the rear springs and ruined them. My problem is, I've replaced them with regular town car springs and they did not hold this big hearse up. NAPA sold me some heavy duty limo springs that won't even fit right on the differential, the coil end is way too big. I've tried looking online for a hearse catalog but I can't find anything. Can anyone point me ion the right direction?