Need help, got a knock.

Use a micrometer and check the the rod with bearing installed and then check the throw on the crank. The difference is your bearing clearance. Is it in the .002 range?  

Had a machinist friend come over today. He measured the rod, bearing, crank, piston and skirt clearance. All checks good. No bent valves. The only thing left that hasnt been checked that would affect only the #6 cylinder, is the cam. Got it apart this far might as well pull the cam.
Quigley  

Pulled the cam out today. Nothing wrong with it. I'm about to pull my *** hair out. What else could make the #6 cylinder knock?
   

My 2 cents- As long as you have it apart, I'd check all the bearings with plastigage,(no more than .0025 clearace, .0015 optimum), and also check clearances on all cylinders, and here's the big one- Are you absolutely positive that you re-installed the piston/rods in the right positions and direction? Oh, and by the way, a cracked flex-plate produces a very similar sound to rod knock, but a little more bell-like. Are there any overly shiny spots on the tops of your pistons or on the edges of your combustion chambers?  
My 442 has a Chevy 350...
I have a '62 292 powered Chevy Pick-Up...

No shiny spots. Piston installed in the right position. Allready checked the clearance and bearing.  Its 5 speed manual so no flex plate. Besides how would a flex plate cause a knock on the #6 cylinder? When you take away the spark on every cylinder the knock doesnt go away but gets quieter. But #6 gets louder.  

Well, the flex plate comment was just answering the earlier comments, not to say you had that problem, I did read the thread.  Is the thickness of the head gaskets any different from before? You haven't changed the heads, have you? What about pushrods, are the in the original order? Cam: what brand, and what are the specs? Since you have it apart, can you try putting your old cam back in for a test? You can buy single bearings, so you might try replacing the #6 Rod Bearing, just to eliminate that as a possible issue. (It ain't easy to diagnose, as I haven't heard it). Also you didn't say what your clearances on the bearings are. I need to know specifics. If you're saying that it gets louder when the #6 plug wire is removed, check the companion cylinder as well, (#5).  
My 442 has a Chevy 350...
I have a '62 292 powered Chevy Pick-Up...

You could even have a weak valve spring causing float, but as stated earlier in the thread, valve issues tend to be tapping, rather than knocking, (outside of actual piston-valve contact). Did you check the mains? Also you haven't mentioned the cam bearings, were they replaced?  
My 442 has a Chevy 350...
I have a '62 292 powered Chevy Pick-Up...

I apalogise if I seem mad. I'm just frustrated as hell with this thing. I really appreciate everybodys help. Same heads nothing done to them. New cam same specs as the old one. New pushrods. New cam bearings. Rings, mains and rod bearings new. Same pistons and rods. I dont have the specs as to the clearances as I had a friend machinist do all the measuring for me and he says all good. Now so far all we have checked is the #6 cylinder. Going to have him check #5. As well as the valve spring.  Thanks again for all your help
Quigley  

What is the color of the #6 spark plug? and you still did not tell us the clearance on the bearings. When you say it gets louder if the plug is disconnected, all the signs are there for an internal clearance problem. Did you mic the cylinder bore and piston. Cant remember what pistons you had but generally cast and hypoteuectic are .001-.002, and forged are .005 and greater.