Dave,
Just noticed from one of your other posts that you are probably talking about the Prestwich Challenger 38. I think we all assumed that you were talking about one of the Aeromarine Challenger hulls. The significant difference being that your boat is presumably a submerged drive setup, whereas the Aeromarine Challengers are normally surface drive.
Behind the prop, and the underneath the hull system which Danny described are probably the most common arrangements for submerged drive setups. Behind the prop can either be one of the purpose built pickups which stand proud and bend forwards towards the prop, or the underneath the hull system can be implemented with the tube cut into the keel line - behind the prop. This kind of arrangement - whether the tube is on the keel line behind the prop, or to one side (or one each side like Danny's photo, where one is for cooling of the exhaust), can usually be cut to be almost flush with the hull - which reduces drag. Any of these rely much more on motion than propwash, so static testing won't really tell you much.
Rudder pickups and behind the transom pickups are usually only used on surface drive boats - or at least with an outboard rudder (in the case of rudder pickups).
Ian