Engine still in the car? How did you support the crankshaft at the front? Regardless, goes to show you can remove the lower block girdle with engine in the car.

Also what kind of wizardry did you use to replace the mains with the engine in the car?

 

The crank was supported it by a hydraulic jack.
The mains you can replace it with the engine still in the car, you just push it out with a plastic tool, but I don't recommend doing it unless you are a mechanic and done this many times before.
So this operation is not the right way, but it can be done.

 

This didn't mess up the plasti-gauge measurment?

 

As long as the crank didn't move I don't see why.