it depends what some people class as an engine rebuild, in my books a rebuild is exactly that, whole engine is stripped, block checked and cleaned up, bores honed, crank regrind, new mains and big ends, new rings, new cam kit, all new gaskets, new cambelt, tensioner, water pump, etc etc.

but providing the pistons and rods are ok you shouldnt need to change them really unless the block needs to be over bored.