When you are ready to weld the cross brace, it is helpful if it is bolted to an engine oil pan so the welding stress does not make the bolt holes become off location.
Have you checked the bolt holes in the oil pan for good threads?
The aluminum pans tend to wallow out quite a bit making the bolt threads useless.
The Aluminum pans can be replaced, using the stronger cast iron pans of the same design.
Also, if the bolts were loose for a long time the pan mounting bosses most times get hammered badly and will not tighten down flat.
Same problem with the cradle mounting surfaces.
just things to check if you haven't already.
One last caution, use adequate length engine to cradle mounting bolts,
BUT not too long!!
Because if too long, when tightening them up tight, you will crack out the bottom of the blind holes, and it will weep oil making you think it is the pan gasket leaking, but in reality, you broke out the bottom of the blind hole.
I've seen it happen a few times to people.