Look in the marketplace for DC3 Enhanced. There are some liveries that include a GNS450 and a more modern autopilot (although basic). It’s a little wonky but with the WT mod it handles like a dream. Did an hour and a half flight at 6,000 feet in the Yukon
That said, the plane was created in the 40s before GPS and Fly by Wire systems. You will be flying like ya grandpappy flew: With nothing but a paper map, your wits and a smidgen of luck
You can reduce prop RPM and fuel mixture once you’re at your desired altitude which can stabilize the plane, but yes you will be constantly trimming the plane or handflying it when not using gyro/autopilot