I don't own a digital or angle torque wrench. Sure they may be a 'nice to have', but a decent manually adjustable torque wrench has done me well for 45+ years. As for angles, they are done simply by using the flats on the nuts/bolts. Each flat is 60 degrees, 90 degress is 1.5 flats, and so on.

I ...

When the plugs in a car I am working on are like that, I spray a little WD-40 down the spark plug recess and wind the plug out and in a little at a time until the threads get slick. Then they typically come pack out ok.

I them put a piece of lint free cloth on a rag and use it to clean the threads ...