Slant six dipstick length
I hesitate to say, as there may be differences between front sump, center sumps and rear sump..
I have a rear sump oil pan, and my dipstick tube broke off.. so I got a V8 dipstick..changed the oil, so I would know for sure how much was in the oil pan,... and then scribed new marks on the dipstick... (no slant 6 trucks at the salvage yard)
What ever you end up doing, as long as it is repeatable and fairly accurate, you should be ok..