Not much on the market to choose from, especially in the 2-1's.
Hooker used to make both scrambler pipes (which are totally bitchin' and absolutely rare as hell) and a low pipe (which I managed to get a set of only after extreme patience and luck).
A company in the 70's called MCM made a bunch of 2-2 high pipes for small displacement twins. These can be found on the 'bay once in a while. A friend found a pristine set for his '69 350 (and paid dearly for them too).
I've got no opinion of the Mac's.
Mostly, people just get a set custom made or slide some aftermarket shorties/megaphones on the stock headpipes. Plenty loud.
Scour the swap meets, race tracks, ebay and cross your fingers.
Honda go sideways!