I am in the process of closing the wings but got to the point I have to wait for some delivery and decided to start some other task in between.

One of the easy stand alone tasks ahead is the mounting of the engine mount.

I had done some investigation before and am quite confident to start doing this job.

I started by finding some large clamps and a piece of 2 by 4 wood to hold the mount in place. The firewall recess is still open so that's a convenient place to clamp.

I test mounted it once just to see if the predrilled holes in the firewall aligned well with the mount. I got lucky and the welding is really well done on my engine mount. All fits very nicely.

Since all holes aligned well, I decided to drill and updrill the first hole without even hanging the mount on. This will become the reference point for leveling.
I drilled it to the size of the predrilled hole and then updrilled to final size. The drill did not go through well and deformed the firewall web a bit. Fortunatly no cracks.

I was able to tap it back and all will be ok.

On the inside, a perfect hole through the steel engine mount.

Next you hang the engine mount. You put one of the bolts in the drilled reference hole and level the engine mount pivotting around the reference point.
Put a level or inclonometer on the lower bar of the engine mount and reposition until reading full level.
Then clamp the 2 by  4 on the front and secure the hole structure with a clamp.
I put some extra duct tape to tempo hold it in place before clamping.

Some additional checking. The inclinometer has a maget in the bottom which is really convenient in this case. Measure left, right and center and all read  0.0.

Did another cross check with my longer digital level with same result. Ready to drill.

Drilled all 4 corner holes. I purchased a bushing to insert in the holes of the mount but since I had some issues updrilling on the first hole, I decided not to use it and immediatly drill to full size using the engine mount bolt holes as drill guides. This worked very well. Use a lot of boelube and let the drill do the job. Don't put a lot of pressure. The image below taken after the second hole was drilled

Rechecked the level with the bolts installed and it looks perfect on all sides.

Finally drilled the two middle holes, installed all the bolts  and checked again with both levels. It doesn't get much better then this...