When I had the 26 apart, I measured how much oil you could put in the sump without it getting whipped up by the crank.
6litres fills the sump to the brim. When the engine is running a certain amount is in circulation (in the oil galleries, oil pickup, head, turbo's etc) and it ran with no dramas. I had done that for years, and also do it to my 34. Never killed an engine, just gearboxes!
The oil I use comes in a 6 litre container so no problems for me
Another point, the stock oil pressure gauge is not quick enough to tell you that you are losing oil pressure for those few brief seconds, when it does it's definately too late! spin a bearing anyone??