I believe that drilling the old upper suspension arm to remove the thread you can fit a stright longer bolt, 15 mm longer than original bolt. IIC the original bolt should be dia 12 mm, but this is the nominal dia,usually they are 11,92-95 so it would be fine to finish the hole with a rimer, to avoid any lash. But as you know the shock bottom rubber bush has a still bush that has to snap fit into the arm. Key point.
In such case you are not compelled to use LE500 longer bolt but you can buy high grade bolts or better Allen 12.9 or even 45H (IIC original are 10.9) it has to be stretched using the right torque according to the bolte grade, a key point will be the self locking nut. Bolt pretensioning is important.
The coupling steel bush/arm is in charge to bear the load, not the bolt, but if the bolt comes loose the coupling bush/arm will be no more so effective.