Replacing worn parts only is what I did. Heck I didn't even remove the engine, but in hindsight I would remove if I ever do one again just to make the rebuild process simpler. I know a lot of guys will moan & groan over the process I chose, but since the engine still ran and showed no other issues I figured what the heck. I replaced the Pistons, Rings, & Rod Bearings with Sealed Power ones from Summit, used a Bottle Brush Hone also from Summit, put in new Lifters from ebay, new Timing Chain/Gear set also from ebay, all new gaskets Fel-Pro only, new Head Bolts Fel-Pro again, and a few other odds and ends. Not sure what I spent since I didn't keep track, but other than the Summit parts I looked for the least expensive options I could find. I hand polished the Crank best I could, cleaned the heck out of everything and then cleaned it again. I re-ground all the valve seats which was a lot simpler than I thought and even though the head was the "dreaded" 0331 version I saw no apparent cracks or cross contamination of oil & coolant so I re-used it. The one thing I did not do myself was putting the new pistons on the rods. For that I found a machine shop and pad about $50 for them to do it which was worth it to me. I cannot stress enough that this is not the preferred way to rebuild an engine, but for my skills/budget it was the best option and so far I am happy with the result and the experience I had in doing it. As far as difficulty level if you are moderately skilled DIY'er and have the space & time to tackle it the job isn't that hard. For me removing/replacing the rear Leaf Springs was more difficult and stressful than rebuilding the engine.