I bet the hardest part is putting it all together for timing. I've been around a few freshly shopped engines early in seasons and they all had crew fine tuning the running gear. All these parts are heavy, awkward, and unique to each engine after 80-100 years of operation. After measurement, fabrication, maintenance, and cleaning, you have to put everything back together, then it gets loaded down with the weight of the engine, water, fire. There are plenty of chocks, bolts, and bearings that can all be adjusted to help this out.