Hollow Thrush Mufflers (vintage?)

I remember running the standard glass packed Thrush like the ones in the pic above but never saw any that didn't have packing. When I turned 16 in 1980 I quickly cut off the stock muffler and put a Thrush glass pack on it. May have only been single exhaust but that 383 still talked pretty good. Thrush glass packs were always my choice as they had the best low rumbly sound and they were dirt cheap. My local Western Auto sold them for $11 if I remember right. When they went out of business in 88 they had an auction and me and a buddy cleaned house. I bought a truck load of brand new brake shoes and water pumps for about $20 and he bought every Thrush muffler they had (40-50 if I remember right) for $20. We made enough money to cruise and party hard all summer on that deal