On a single turbo the manifold joins all four branches into one and routes the gases into the turbo. Now, I assume that a twin turbo puts cylinders 1 and 2 through the first turbo and 3 and 4 through the 2nd turbo. Both then connect to a single exhaust.
There are 2 intakes or one intake spilt into two which then goes through both turbos and then join back together and into the inlet manifold.
Is there any reason why you can't fit 2 Turbos to a C20LET?