VAX was a heavily microcoded design, so there wasn't really "silicon level" implementation of VAX instructions themselves - the microcode decoded the instructions and set inputs to execution units, and unlike some modern microcoded designs, there was much less hardwired implementation AFAIK
At least some VAX models supported user-supplied microcode and thus a customizable ISA. This could be used, for example, to implement a Prolog abstract machine directly on the CPU[1].
