Obviously it's nostalgia for me, but timing lights, distributors, points, carburetor ports and butterfly valves, you could really see into the mechanisms. Hell, my dad (who was a master mechanic and worked on cars and railroad diesel engines to put himself through college) took a drill to the fuel injectors on a shitty 80s Chrysler engine that was knocking and stalling when cold (no amount of adjusting the choke could fix it). I drove that POS in my college years and never had a problem with it.