I've been following along on this post. FIRST, back on your rockers, a previous poster was correct. There are "rights" and "lefts" and you have to look very closely, but when installed correctly each pair of rockers points "inward" ever so slightly.
Also, I can't remember off the top of my head, but the oil holes on the bottom of the rocker shafts, have a definite orientation. When bolted to the heads (holes down) they point "slightly" towards the carb or away from the carb... can't remember, but it's noted in the factory service manual. IF you're are pointing the wrong direction, take the shaft off & turn it around the other way (left vs. right) & all the rockers/spacers have to be switched around the other direction.
NOW back to your squeal. Your stethoscope told you it was DEFINITELY in the timing cover area. Look very closely for metal scrape marks where something is hitting. I can't see any scrapes in your picture, but look close. There's not much up there. All I can think of that's up front is:
a) oil slinger loose or hitting timing cover
b) cam walking forward like a Chevy & hitting the timing cover
c) balancer moving around.
d) clearance issue top cam gear vs. timing cover
e) mechanical fuel pump push rod
f) maybe something weird with the crank pulley cocked sideways on the balancer
If worse comes to worse.... and I don't think this is the case because of your good oil pressure.... something in the front main bearing and/or #1/#2 rod bearing. You can drop the pan from under the car by just dropping down the drag ling (remove at pitman arm + idler arm & leave attached to tie rods so alignment will still be OK).
As for tightening the crank bolt. Definitely use an impact wrench and see if you can find a way to jam the flywheel or ring gear (inspection cover or starter hole?) By now, "somebody" must have invented a tool to do that, but I don't know of one personally.
Oh yeah, and change out that woodruff key