The link says nothing about proposal. 
That is a true statement. That was my (hopefully incorrect) assumption.You can submit your candidate block back as a proposal, and see if it would accept it.
I was hoping that this was the case but I couldn't find any examples on the use of "proposal". I couldn't even get "proposal" to get accepted syntactically. I figured that getblocktemplate wouldn't go through the pool software but what I think I'm understanding you to say is that I can take the output of the pool software and feed it back through getblocktemplate.
If that is correct, conceptually how do I get my block out of the pool software? I guess I could write something that would send the output to a file but do you have an easier way in mind?
Then, and again these are assumptions, how does that file become input to getblocktemplate (or I guess if "proposal" takes a string as input, I'd cut and paste the gigantic block, but again I can't find anything beyond the documentation for "proposal", no examples (and even the examples at the bottom of the documentation (link below) for bitcoin-cli seem syntactically incorrect)):
https://bitcoincore.org/en/doc/0.18.0/rpc/mining/getblocktemplate/
So I guess the biggest help would be if you could help with the conceptual and point me toward uses of "proposal" e.g., examples.
Thanks.