This is largely contradicted by the (pre RISC-V) MIPS editions of Patterson & Hennessy, Harris & Harris, etc., which teach you how to design a MIPS datapath (at the gate level.)

Regarding silicon implementations, consider that 1) you can synthesize it from HDL/RTL designs using modern CAD tools, and 2) MIPS was originally designed to be simple enough for grad students to implement with the primitive CAD tools of the 1980s (basically semi-manual layout).