Dont rule out the 5.0 thats currently in the car. I believe that 85 was the first year of Factory roller cams and Multiport EFI, so consider a good duel exhaust, some high flow cats(All 4), a Shift kit for that POS AOD metric, a Performance chip, and take a look at your rear end. Some grand marquis came with limited slips, some diddnt. This car with a good freshining is capable of lighting the tires in stock form, so if you have a small budget, look to improve whats there.