The only advantage to using aluminum for a FW spacer is ease of machining. And, .. in the case the 4x4 labs unit, they can make it out of the otherwise scrap material found in the center of the bell housing spacer plate. They can also make the FW spacer first then go on to making the bell housing spacer without having to set material back up.

I don't see any threads in the Ford side of the adapter, they should have been put in when it was on the mill. Don't try to make these threads by hand, helicoil taps are generally plug taps and are not easy to start by hand if you want a straight thread. Set it up in a mill or drill press to at least get things started.

Tilted holes put bolts in bending rather than just tension and can lead to bolt failure.

While we are on the helicoil subject. Be sure to place the end of insert 1 to 1 1/2 threads below the surface on the tension side ( the side towards the bolt head ) otherwise you run the risk of lifting the insert or even having the aluminum start to crack. I've seen non helicoil threads in aluminum crack in a spiral to where you end up with an aluminum spring.