Is there a hole in the pan for a tube? If so, go to any speedshop or even Autozone and pick up a chrome universal one. You might have to do a little tweaking to get it to fit the hole, but it can be made to work. To calibrate the dipstick, change the oil, add exactly the number of quarts of oil this engine pan is supposed to be, and then insert the dipstick. Pull it out and scratch a line on it at the full mark with a hacksaw or similar.

I've done this a few times and it works fine. Sometimes you have to use something like JB Weld as a caulk to get the new tube to fit tight in the hole.

Don