Mike. I think what Stucco was/is saying is....he doesn't use the Affnan's......so he doesn't want to mis-lead you on them.
The (basic) differences between the two bells are....Affnan's 'do not' have a little hose, going to the top, that breaks the suction....standard bells ... "DO"
Affnan's have a reducer/bushing sitting on the top of the stand pipe. Standard bells...'do not' have that on top of the stand pipe.
The bushing is the 'key'....something to do with fluid dynamics. Didn't Affnan say he was an fluid engineer (?)
I don't remember Affnan adding any traps or slightly running his drain up hill, at the end of the run (?) ( Then again, I don't remember what I had for dinner last night either... )
Bell size (?).....what I did is .....I took the size reducer/bushing I wanted to put on top of my stand pipe....and tried different pipe sizes, till I found one it would fit inside of....
You won't look any sillier then the other customers in the pipe dept, at home depot. If an employee asks what your doing/or do you need help...ask him/her if they have an hour, and you'll gladly explain.... I get home a lot quicker using that line....
Drains....You still may be able to use 2 ", by only hooking 2 GB's to a 2 '' drain (the other 2 Gb's to another 2" drain) ...independent of each other.
The odds of 2 GB's 'kicking off' at one time is slim. You said you 'already have' the 2"
height....Mike, I don't know ,if you said how long the drain 'run' will be....? You only need 1/8 " of fall, for each foot of 'run'. Of course you mentioned the fittings coming out of the Gb's, add up, on the fall, too.
Wish I could be more help...