Looks great! There will be a spacer over the springs in each fork tube. Measure the spacers, that will tell you how much over stock the tubes are. fyi, stock do not have the spacer.
Correct, and as an FYI there is about 1/2 quart that really doesn’t get drained. After draining, I sometimes spin the engine with oil filter housing off just to the point oil spitting slows down.
Yes, a slight drop in compression. The 77-78k; 75-76f have about 1/4” flat border around the edge and then a slight dome. You should be ok with early k pistons. A good machinist could make up the difference in compression for you by decking the gasket edge for you.