The 13c hotside attaches to the downpipe via a concial flange. This is a dry fit without a gasket. The collar which is free to move on the downpipe has three bolt holes in it and the studs screw into three holes on the hotside through these holes and are collat tightens onto the union when the three nuts are wound down. Therefore if you wish to replace the 13c with a non-conical housing turbo you will need a new exhaust downpipe with a flat or angle flange.
A conical flanged 15g turbo then is a direct drop in replacement once it has been "reclocked".
Basically the coldside outlet (for boosted air) points straight down on the 850's and V/C70'S. However on the RWD Volvos it points upwards. The coldside compressor housing needs to be rotated to 1.05!
If you have a look at this link it will appear clearer!
http://www.turbobricks.com/forums/sh...ad.php?t=83929