I have a 97GT with an offroad H pipe and factory mufflers. I think it has exactly the sound you are looking for!
The factory mufflers were tuned to sound good and like a muscle car should. Make the most of the work ford already did by getting rid of the (6) restrictiving and muffling cats.
I would not recommend combining an off road H pipe with aftermarket mufflers, as this would be quite loud. But with the factory mufflers it really is the perfect sound. Definately go with an H pipe for the old muscle car sound. Getting rid of the 6 cats makes each exhaust pulse more noticable and more aggressive sounding instead of smearing all the pulses together. With the factory mufflers, it will defintely be quiet enough and not obnoxious at all.
Mine starts mean. When I start it, most people not familar with the exhaust note will say 'wow', but it is quickly smooth and quiet. At idle-2000rpm, it is nice and quiet, just slightly louder than stock. It is certainly easy to sneak out of the neighbor hood in the early morning hours. From 2000-3000, it is a bit louder, but NEVER has any resonation. I hate resonation with a passion and that is why I choose to keep the factory mufflers. Beyond that, it isn't loud at all, but just sounds nice and like a V8 should.
I think you would be very happy with an offroad H-pipe, but you'll need to build or buy MIL eliminators to prevent the check engine light. This is extremely simple and cheap too. The only difficulty is emissions/inspection. You know the law.