The muffler was there to smooooth out the gas flow through the system. The compressor output will have pressure pulses due to how it operates, especially at lower compressor rpm.
When my '77 Camaro was newer, one spring day I turned the a/c on for the first time in a/c mode and at certain engine rpms, got a new harmonic vibration that seemed to be coming from behind the instrument panel. Only with the compressor running. Diagnosis indicated that it was due to the fact that that factory a/c system had no muffler in it, BUT the more upscale Firebird models DID. As did almost every other GM factory a/c system, but not Camaros.
So, the shop foreman advised of an auto supply to go to get the needed muffler and clamps, which I did. I'd already looked at the Delco A/C Illustrated Parts catalog for information. Got the new muffler installed and all was quiet again.
That was with the GM A-6 (6-piston) compressor that generally operated very smooth and quiet. Obviously with more even pressure spikes (or less intense) pressure spikes than either the Chrysler RV-2 or Ford Tecumseh 2-piston (BIG piston, by comparison) compressors. I suspect the newer-design Sandens might operate smoother than the older compressors?
It could be that the receiver/drier might act as something of a "muffler", but maybe not, depending upon its placement in the gas flow system? Once everything is installed, might be a good idea to design-in a length of hose (compressor output) where a small muffler might be installed later on?