A couple of updates...

I removed the valves from the passenger side head last night. Per the machine shop only 1 of the 7 identified leaking valves are on this side. I tried filling each of the ports with water per disassembly just to see if there are any noticeable leaks. Only one (the identified one) showed some moisture seeping around the valve so that seems to align with the shop. Seems like using water or gas will only work for a serious leak and I am guessing that air or a vacuum is needed to test accurately.

Not too put a damper on this project, but a known YouTuber Toyota mechanic who recently opened a shop here in Illinois told me that the 1GR-FE heads can not be milled due to the VVT-i system. He said if they are warped he normally recommends replacement. I had spoked to him by over the phone by chance as I was calling to cancel a prior inspection appointment that I had setup a few months ago when I was trying to determine where my coolant loss was coming from. His shop appointment times are hard to get.

I can't turn back at this point and need to keep moving forward but you can definitely see that opinions vary on this topic. I also was wondering if the timing cover will have an issue with alignment once the heads are milled. I'm guessing they should still be okay assuming the material removed is very minimal. Nonetheless that popped in my head yesterday after my phone discussion.