Doing further review after comments on the prior page, it appears that the factory may have set the oil level bit too high for the Twin Cam engine, or there may be an error in he Workshop Manual and/or Driver's Handbook.

On 6/8/2020, Mick Anderson wrote:
"Does someone Have the sump off their engine and can make few measurements? Using water in their sump can they measure the depth of the water after adding 7.1 Litres and then 7.42 Litres. The Workshop Manual states a capacity of 7.1 Litres and the Driver’s Handbook states 7.42 Litres (both have the filter of 0.28 Litres capacity subtracted). The critical level for con-rod clearance is 77mm".

Jonathon Tucker replied:
"I have checked a sump I have, and 7.4 litres gives a depth of 80 mm of water and a clearance of about 42 mm to the sump face"

Paul Deslandes wrote:
"Assuming a linear relationship, reducing the volume of oil to 7.1 litres would reduce the depth to 77mm".

And more notes from Barney:
I would say the oil cooler does not empty out when you drain the sump, so after the first run, volume of the oil cooler is irrelevant when changing oil. Volume of the oil filter is important.
80-mm fluid height would be just touching the bottom end of the con rods, which is a no-no. 77-mm is only 1/8-inch lower, so may also be bad, Going up hills or down, and hitting the accelerator or brakes causes front to back slosh, which may get the oil level up to the con rods. However, if you start with 77-mm (maximum), and then start the engine, some oil will be pumped up into the engine with slightly delayed return, so the running oil level may be slightly lower. That may be okay, as long at the high mark on the dipstick is no more than 77-mm from the sump floor, at least 44-45 mm below the block bottom surface, and you absolutely never exceed the high mark when topping off. For those of us still using imperial measurements, that means oil level should never be any higher than 1-3/4-inches below the sump flange.
Distance of the high mark below bottom of block is important, regardless of depth of the sump (alloy or sheet metal). That would be the guideline for checking height of the dipper tube and position of marks on the dip stick. I think a good section drawing showing height of the dipper stick tube and position of the dip stick will be important.
Assuming we are about to come to agreement on this, I would be happy to post it on my web site. This is looking like 7-liters to fill the sump (if it was fully drained), plus a little more for top-up when you also change the filter.
There was a change with the pushrod engines where they raised the Low mark on the stick without changing the Full mark. End result is only about 2/3 quart range between Full and Low marks, so if you never let it go below Low, you can only add about 1-pint at a time (as 1-quart or 1-liter above the Low mark would be overfilled).
Pretty sure this change on the dip stick markings happened before the change of design in the oil pump pickup arm and screen (October 1958), which reduced inlet restriction and the tendency to cavitate at high engine speed. That may be another example of implementing the wrong fix, before figuring out the true problem. I believe the Twin Cam never had the earlier design of pickup screen, so this higher "Low" mark may not apply to the Twin Cam engine.