For the 55-57 235 motors the bb is TDC for timing purposes.
.
.
Others have a bb but also various markings for setting the timing, a triangle or line for instance where the timing is set some degree in advance (I forget off the top of my headbut that might be 59 or something later) as the timing settings changed from time to time, from application to application, and even depending on whether the car or truck was a Canadian model.
55-57 235 cars and/or truck 235 and/or 261 BB is TDC - is that the timing spec is TDC for those engines in those?
My understanding us the bb/ball is TDC/TC in any year where a ball is present on the flywheel, but the ball is not necessarily the timing spec. TDC (the ball) was the timing spec in some years.
Regarding no ball in a flywheel, I have also seen such flywheels on later USA 235 and/or 261 engines (I do not know the years/years).
UC/UDC is marked and a timing mark is scribed/labelled on those flywheels.
