Can't help you with the length, but the factory spec for a 1980 360 engine is:

1) 4 qts w/o oil filter change
2) 5 qts w/ oil filter change

Here is what I did to re-establish the LOW & HIGH levels (following the original engine start-up, break-in, etc, etc), given that I replaced the stock tube with the shiny (chrome..lol) MP kit (tube & dip-stick).

1) totally empty system, add 4 qts
2) start engine, shut off after a couple of minutes, let oil drain back to the pan
3) pull dip-stick, clean, re-insert and note the oil-level
4) mark the oil-level as the LOW spot on the dip-stick, I drilled a small hole in the dip-stick to give me that mark
5) add 1 qt to bring the total level to the spec 5 qts
6) repeat #2 & #3 from above
7) mark the oil-level as the HIGH spot on the dip-stick, I drilled a small hole in the dip-stick to give me that mark