Pat, yes - you can simply remove the factory muffler and install an aftermarket muffler. You may need to install a 'filler' if the new muffler is shorter than the factory one. That is what I did to my truck (scroll up to see the details).

The 50-series on mine has a very low 'burble' at idle, sounds throaty during acceleration and roars when I stomp on it - but not to the extent that you can hear it for blocks around. Keep in mind that tip size will affect the tone of the exhaust to a certain degree.

Tom in Tacoma

 

I have an Expedition 5.4L with Flowmaster 70 SUV, dual 2.5" exits to 3.5" tips and it sounds great. Nice low rumble, but comes "alive" when you get on it. Definately not too loud, but sounds "meaty". I actually switched from a 50 to the 70 because the 50 delta flow was too loud in the cab.

cust_expy
'00 EB Expedition 5.4L
18" TSW wheels, 285/60/18 Bridgestones
Flowmaster 70 duals
Superchip
K&N
Stull Billet Grill
Hellwig Anti-sway bar