I just put some 2.5" $40 stainless mufflers on my 5.0 Mustang that fit your description perfect....they are essentially glass packs but are not straight thru they are rectangular and the pipe is offset from one side to the other as it goes thru the muffler. They are not loud, but have a nice sound.
https://lmr.com/item/JES-MF1236/Jones-Max-Flow-Performance-Muffler


Take care,
Rick
68 Coronet R/T 440 & 68 Charger 528 Hemi,and 5 Challengers! 6 cyl, 318, 360, 383, 451