I try not to buy every tool in the catalogs, but some become indispensable.  A piston ring clamp, found in most auto parts stores, is a mighty handy tool.  There are special wrenches for Continental engines for installing the cylinders nuts—“heavy-duty cylinder base nut wrenches”.  Aircraft Tool Supply has an Aircraft Engine Stand for assembling the engine on its propeller flange keeping the other delicate parts away from the banging and denting of other hard surfaces.  (I found one from a fellow builder, a little different design, but the same idea.)