They're just a strip of mild flat bar.
what bolts?
Atf or plus gason the original vice bolts holding the vice blocks on and bolts holding the quick release mechanism undrneath..
On the Engineering vice, it is a 1" flat bar. Metric will fit. But may cause binding.
A dress will sort that out.
The wood working vice, remove the wood.
Soak in Citric acid, vinegar will work. But will smell.
Any fixings can be removed, with traditional methods.
Heat.
Oil
Plus, time.
On the engineering vice, the fixings will be either UNC or more likely Whit.