Cummins M11 ISM turbo differences

I bought an ISM motor with a HX50 turbo which does not have a wastegate. The motor is a year 2000 ISM and the head serial number and ECM number say it should have a wastegated HX55. So my question is how boost is controlled without a wastegate, and also whether it is possible I have a different shortblock than what I should, with the correct head and ECM attached. If so they would have had to have used the new motor's manifold because it matched the HX50 and the HX55 has a different flange. If that is the case could there be piston changes that might result in a lower horsepower rating? I bought it as a 425 hp 1550 tq but after finding that the turbo is different I am worried that I have a lower hp motor.