you sound like what I am going through. However mine has a few other issues that I have taken care of with the same results. i replaced my intake gaskets since they were rotted. i have a distinct misfire on my #6 cylinder. it backfire and pops through the carb. I put a brand new carb on and a Accel HEI Dizzy. i took the intake off adn found the intake vavle on #6 doesnt close all the way and allowing everything to come through the intake. A compression tast was run on it a few years back and it was steady with the others at 120. The #8 was about 90. So it is trickling through the head it seems. So I am in the same boat you and your friend are in right now.
As for plugs. i am running Accel shorty plugs on my 350. part #8199. they run about $30 for all 8. U-grooved. I have gone through a ton of plugs only to have them either foul out or the wires burn up from the headers. I also run accel 8mm HEI wires. I buy the custom set so you can run them how you want. You get great spark if you run them together. Hopefully that helps a little