the eng,that could

Try periods in your sentences. It makes reading easier.

The 273 in it's first two years have odd intake angles for the intake manifold. Changing heads to later years fix this issue. The intake bolts are also thinner. Any small valve 273 or 318 head will work with the 1.75-1.50 valves.

Some 273 did indeed come with adjustable rocker arms. Though any aftermarket will bolt in as well. Other than that, being an early engine, the timing cover and water pump style are different than the later years.