Accurate tests for Cl can be obtained with Ben's kit (the best) or a Taylor 2006 kit (orderable online) Ben's kit will get you speaking the same language as all of us and is well worth the wait.

You can get a reasonable idea of your Cl level by diluting your test water with distilled water. So, if you dilute by 50% and get a reading of 5ppm, your "real" reading is 10ppm. It's not very accurate and it's a "stop gap" method but you'll get close enough for this purpose.

You are slightly misinterpreting the "best guess" chart. The CYA does not affect the total Cl....the Cl is simply less effective at high CYA levels. That's why I'm suggesting 30ppm of Cl.

Since you're leaving town, get the 8 gallons of Cl in there tonight and get the process started. I have a feeling your water will clear before you leave. See if you can get a neighbor to put in small jug of Clorox each evening and run your pump for 8-12 hours each day....that'll protect your pool while you're gone.