I would like instructions to find what I can unquestionably know to be the truth, now.
Here they are:
1) You are using the wrong tool (your fine mind) to discover the truth. With that tool, and its infinitely discriminating criteria, you will never find the final truth. Never. Never.
2) Considering #1, your fine mind can, however use an ancient phrase, which, from your vast reading is "neti, neti" - meaning "not this, not this." Which is to say that something the mind can understand, recognize, measure, criticize and manage cannot be the truth. This reality is why Ramana's enquiry "Who am I?" works. To discover who you are using the mind has the benefit of ending the use of the mind for the purpose of finding that truth of identity, perhaps after countless hours and months of trying. See #1.
3a) OK, having swallowed #1 and #2 for at least the duration of this post, what else is available? Meditate.
3b) There is that thing called "the heart." For serious thinkers like you, the heart is perhaps best understood as "intuition." For people like you who appreciate the masculine approach (cf. Barry Long), the next step, trusting intuition is harder. It's keystone first step is called "surrender." There is a Zen phrase: "To yield is to conquer." Yielding is a 'stand down' order to the mind. That, is, as a reminder, one of the benefits of regular meditation.
3c) You are probably familiar with Jung's principle of synchronicity (see Wikipedia for a fair review.) As part of the yielding, and fine-tuning your antennae of intuition, become aware of the daily events in your life...are any of them actually pointers? Is there a "message" from the universe trying to get through your big egoic mind, rideforever? (I ask this with great respect, sir....I had a big mind in the driver's seat for 60 years. Harvard, many honors, significant jobs, etc. Learned lots of compelling partial truths with it, too.)
4) The truth will arrive as a 'recognition,' which varies in intensity. It will result from Grace. All seeking will end, but all resolving will not end. Resolving continues, probably for years.
I think Rupert Spira's "Presence, Volumes I and II" represent the best current work on nonduality...he talks about the seamlessness of experience. Arguing about concepts is not the path to awakening.
A person is not a thing or a process, but an opening through which the universe manifests. - Martin Heidegger
There is not past, no future; everything flows in an eternal present. - James Joyce