You should be able to use the center section to the compressor side of the turbo in your 16 cm housing. I do believe that you will have to remove your exhaust wheel and put it on the 40's shaft. I would highly recommend to have that balanced. Other wise I would run the T-4 housing.
You can use an adapter to run a T-4 on your manifold. Or the proper way to do it would be to get a Big Foot 3piece manifold from ATS with the T-4 foot already on it.
If your 40 has a T4 it's probably a 19cm unit. It's gonna be a pig unless it's on an auto.