My 10c worth, drill the xm to match the new bolt size 10.38 , or use Nolathane inner bushes.

Why would  you drill out the cross-member ? Sure it's the easiest fix but once done there's no easy way of going back to the 'correct' arms later on. Either exchange the arms for the correct ones/ get $ back and buy correct ones elsewhere or in my opinion the easiest solution would be to put the correct bushes in.
 
Failing pale blue bushes would be the 'Noltec' branded ones I'm guessing. I've seen 5 sets of their adjustable top mounts turn to dust including my own.  But I liked the floating design (independent camber & castor adjustment)  with the little bit of urethane 'give' rather than being a completely rigid design. So I got mine recast with a proven urethane formulation.  Just poor formulation by Noltec in the first place. I've got K-mac top mounts of similar design in my other car, still fine after 25+ years!
 
SFE

Why would the 10.38mm diameter be a problem?
Aren't all suspension bolts, including the cross member bolts supposed to be tightened up tight when the car is back on the ground and suspension settled with the weight of the car on it?
Aren't the cross member walls designed to crush in against the inner control arm sleeve when the bolt is tightened?
The pivoting (up and down) action of the lower control arm is achieved with the flex in the rubber, not the bolt.
 

Machine a section of steel with 3/8 hole, maybe ream the finish, loctite to a 3/8 rod and machine the OD to size and polish to fit the final size,, heat the sleeve to remove from the rod, then loctite into the bush. Probably no need to be hardened.