All glass pack mufflers burn out with heat; so the further back on the tail pipe you can install them, the longer they will last. Greater life span is obtained by using them as exhaust tips on a straight exhaust pipe that exits out from under the rear bumper.
All glass packs are straight through "mufflers". I use the word muffler advisedly as they are used in racing because they neither muffle nor restrict exhaust flow when kept large and short. The only resistance they offer to the exhaust flow is from the louvers punched in the internal pipe to ventilate it that hang down into the exhaust gases to restrict laminar flow. If you run a three inch glass packs with an adapter to fit it onto your 2-1/2 inch pipes you reduce that restriction promoting both the amount of noise and the rate of exhaust flow.
Chevrolet only used a glass pack muffler as optional equipment on only one car; the Corvette, in the form of side pipes. The mufflers where five feet long and 2-1/2 inch in internal diameter.
I had a set (GM called them chambered exhaust mufflers) installed on my Baldwin Motion Phase III 1968 Camaro and they drove a twenty three year old me nuts with the noise (I could hear the same level of noise that every one I drove by heard, which doesn't happen when the exhaust exits out from behind the car). I took them off and then used the actual high performance muffler that Chevrolet used on the Corvette in 1968 and it was also used on their early highly successful turbo charged Corvair. That muffler offered the same flow rate as the glass packs, but with half the noise level.
Flow Master copied this design and offered them for sale as their 40 series muffler.
Here is what a standard Walker automotive muffler looks like inside.
The gasses enters at the lower right hand side pipe and runs into the wall of the back of the central chamber through a reduced diameter pipe inside the muffler. It then has to go into the pipe with the perforations and flow through to get up to the top pipe by again hitting a wall in a closed off front chamber. The middle pipe with all of the holes in it cancels out the high frequency noises. Notice that there is blind alley on the left off the central chamber, that goes nowhere. That is to reduce the lower frequency noises. The gap in the top pipe is so that exhaust pulses (momentary pressure spikes) cancel each other out as the majority of the gas has to take a longer path through the muffler. This is why they are so restrictive to exhaust flow. The muffler made by Walker, muffles almost all noise that enters it and evens out the flow of gas to a continuous stream with no pulses or pressure waves (you hear those pulses frequently in school bus exhausts because of the long, long pipe from the engine to the muffler way in the back of the bus away from the funnel tank magnifies the pulses through harmonic resonance).
Note that the gasses have a nearly straight shot through the baffled exhaust muffler made by FlowMaster (you can not buy original GM mufflers for the Turbo Corvair or early model Corvette only repops). The muffler is based upon echos. Just as an echo dies away the noise of your engine is canceled out but the gas flow is not restricted in the baffled Flow Master design.