WOW! 20 year old Bullitt with just 33k miles. You have to go beyond the Ford 30k recommendations for a new car and get into PREVENTIVE MAINTENANCE, to reduce the potential for oem parts failure.
Total fluid changes of brake, oil, cooling, tranny, diff and power steering fluids.
Replace oil, tranny, air and fuel filters.
Cooling and heater hoses. Go with silicone hoses if available. Replace the infamous plastic 3 way junction of the heating/cooling hoses with a brass coupling, which will last forever.
Replace the Brake lines, from the oem rubber to braided metal lines. Will last a very long time. Also check the brake pad's condition. Pads age out even though they have material left. Check the caliper piston seals.
Yes to sepertine belt replacement. Sucks if 20 year old belt breaks on a roadtrip to Boise Nats.
Have your mechanic inspect all the suspension bushings. The rubber will be aging out. Also close inspection of the driveshaft U joints. Again aging out.
Monitor the Bullitt's parking spot for fluid spots, which indicate seal leaking.
With the 20 year old Bullitt, you have be in the preventive maintenance mindset, beyond just the mileage.