I had a similar challenge recently during the rebuild of my 53 TF. Initially I planned to simply drill out the existing BJ rivets and replace with nuts and bolts etc.
On closer examination of the lower wishbones the plan changed
as one of the wishbones, whilst looking OK at a glance, actually looked like this:
When I removed the wishbones I found that they are effectively two thin pressed steel halves stitch welded together which you can actually blow air through as they aren't sealed from the elements!!
Given that my TF has only done 40K in its life I would suggest that this may well be the life expectancy of these cheap MG parts.
So it may be that if you're still running around on original wishbones it would be more cost effective, and safer!, to simply fit new units c/w new BJ's.
I bought new units and then sealed all around the seams in an attempt to preserve the internal surfaces from corrosion.
Good Luck
Squashman56