My until someone chimes in with a measurement.

The tube itself is nothing special, just a length of hardline. If you know you have the correct amount of oil in it based on what you put in, you can make your own tube and adjust it (re:cut) to where the dipstick reads correct.

I did this with a truck I dropped a 440 into using parts from a 400 (the tube went MIA during tear down in my case). Sorry, this was back in the '90's, truck is long gone.