Engine sounds great. It'll sound even better when under load doing some serious work.
Lift arms go down under gravity. I have AG90 oil in my back end, which is a bit thick for the Super hydraulics, so when the oil is cold my arms take some weight to make them go down (when in work the oil gets warm and the arms drop easily). The drop control knob also needs to be fully wound out if there is no weight on the arms.
Re the drop control knob, it was really useful with the power harrow and the reversible two furrow Ransomes plough. It allows you to push the quadrant lever down quickly without the implement hitting the ground with a thud.
Setting up the hydraulic lid is an art. I have friend who worked on Majors and Dextas for the main Ford dealer in this area in the sixties. He set it up for me. You've got a pretty nifty push/pull sensor mechanism on your tractor which will lift or drop the plough according to conditions. Works a dream when it's set up properly.
Best
Adrian
Dandy Dave!
looks and sounds good though i'm not sure about the front grill
I started my Power Major a few days ago after sitting all winter. She started straight up and sounded just like your tractor, so you did something right. 
Dandy Dave!