We are thinking that we may have a problem with exhaust back pressure in our new 60 HP Beta engine

We can measure the pressure in the wet exhaust, just downstream of the water injection point with a home made manometer connected to a 1/4" copper tube stuck into a hole drilled in the rubber.

However, engine vendors quote acceptable back pressure values in the dry exhaust section. Neither our old Volvo nor this engine have any connection point to measure the pressure in the hot, dry section. Since the gases are hot, this will require a suitable gauge.

Does anyone have any idea how to estimate back pressure in the hot dry part of the exhaust system by measure in the wet part as above?

Does it even matter? If the back pressure in the wet system is below the manufacturer's dry section recommendation, does that mean that we are OK