BE9T pilot reported airspeed and altimeter discrepancy's on first flight following maintenance inspection. Pilot elected to climb through the overcast and landed uneventfully at destination.

Narrative

Upon picking up the aircraft to ferry back to my home airport and after having just come out of a complete phase inspection including a 91.411 altimeter and pitot static inspection; I was departing ZZZ in a 1100' overcast ceiling with 10 miles visibility. During my climb passing through about 7000' MSL I noticed a discrepancy between the altimeters and airspeed indicators from pilot and copilot sides. Being in IMC at the time and expecting to break out into VMC shortly; I decided to continue the flight rather than attempt an IMC approach back to ZZZ. I broke out of the IMC at around 9000' and it was clear VMC above. The alternate static air source didn't correct the problem. At cruise altitude I inquired with ATC a few times along the route and they confirmed that my altitude was indicated as was assigned; so I decided to continue the flight with the pitot static issue that I was having and determined that even though there was a discrepancy between the two left/right indications; that the pilot's side seemed to be indicating the correct altitude. After talking with the maintenance facility and another avionics technician; I suspect that neither may have been indicating correctly; and that my altitude actually may have been higher than indicated even though ATC was agreeing with my reporting.