My question is what flange for the exhaust housing does the stock turbo use for the exhaust manifold on the 850R?

T3, T4, or other?

 

Other...

1994 and 1995 model years use a conical style flange (turbo to exhaust downpipe)
1996 and 1997 model years use a straight style flange (turbo to exhaust downpipe)

More info here on turbo to exhaust downpipe...
http://www.quickbrickmotorsports.com/products.html
http://www.quickbrickmotorsports.com/prod_dpflange.html

More info here on exhaust manifold to turbo...
http://www.quickbrickmotorsports.com/prod_manifold.html

 

is the exhaust housing on the TD04 15G 7cm2? what I'm trying to say is... will I be able to swap the stock exhaust housing on the 15G for a 16G so it will fit my mitsubishi header?

 

which mitsubishi engine 4G61, 4G63, 6G72 or other?

 

4G63

 

Volvo 850 Turbo has DOHC 2.3L with Mitsubishi TD04HL-15G-7CM2

If you can't find the answer here...
http://www.turbochargers.com/Turbos/...rbos.htm#Volvo

Then, ask
http://www.turbochargers.com
http://www.forceperformance.net