My dad had an independent garage after WWII through the fifties, and could make the old Chevy sixes and Ford flatheads sing.
I bought a really nice forty Ford in the early seventies. It ran and sounded so good when I bought it, you almost had to look at the oil pressure guage when sitting at a traffic light to ensure that the engine was still running.
My dad said that the valves weren't too bad, but they weren't exactly right. He couldn't stand it and ground them by hand and adjusted them. It was amazing. After he was done with that and setting the vacuum brake on the distributor(remember that), you absolutely did have to look at the oil pressure guage to ensure that the engine was still idling.
These engines were simple in a lot of ways, but it took mucho skill to really make them right.
Sorry to post this here, but I couldn't help myself. I hope you enjoyed it.
Have a great day,
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in