Re: 164 Cloverleaf 24v Speedlines - Stud Removal ideas please!
As you say, the bolts are plastic fake ones and, AFAIK, don't unscrew.
I'm sure I've read somewhere (possibly on this forum) about someone finding a firm who successfully refurbished them, without removing the "bolts".
I ended up drilling mine out, before having them refurbished. I was going to replace the plastic bolts with M7 allen-headed bolts, glued into the holes, but never got round to it.
Try looking on some of the American forums (164Digest, AlfaBB) to see if anyone's posted there.