i was thinking about doing this exact same thing a couple of months ago (i have the chicken scratchings to prove it).
my plan was to have one inlet like yours, but almost "T" the outlets so that two stockers could be mounted at a 45* angle from the engine. get one 2.5" 45* bend for the first turbo downpipe, then a 2.5" straight with a 45* piece coming off for the 2nd turbo.
once the two join, get a 2.5" to 3.5" adapter and run a 3.5" dp (provided there's enough room).
then, run either an external limited to 12psi, or two stock wastegate actuators at 12psi to keep the turbo in it's best efficiency range. the only math i couldn't figure out was what the output of two turbos would be. do you add the "cfm output" together to get total output?
finding room might be a problem, but i think it would look pretty sweet. reminded me of the tt setup on supras (?) with both of them 45* from the engine.
just my 2 cents