One of the best signs of a worn motor that might need major rebuild is hw much ridge you have at the top of the cylinders. If you can borrow a micrometer and measure the bore diameter and them the ridge diameter you will see how much wear there is on the cylinders. Specs for cylinder diameter are available online and if cylinders are worn too much rebuilding the top end may only force compression past the rings into the crankcase not to mention oil consumption. If the engine has high miles (around 200K) you might also want to look at rod bearings if your removing the pan. I have seen many of those motors knocking due to worn rod bearings.