Is it a MHI turbo Big 16g etc?
Has it still got the pin in the CHRA housing the slots into the corresponding hole? (turbine)
I just changed my turbo and Mine was an upgraded Big 16g and the pin was missing. I had the same problem and the actuator wouldnt bolt up at all (well one bolt hole wouldnt) so I remembered when I put it together that the pin was pissing and I had previously marked the 2 matching points on the old turbo (CHRA/turbine) and it was as close as I could get it this time.
So in other words, loosen the bolt on the clamp that holds the turbo together( CHRA to turbine side and clock/rotate the turbo anti clockwise if I recall.....(IF the pin is indeed missing)