Keith
too late for CO Litmus tests if heads are off. Keep it in mind if it happens again. A cheap, quick and effective test.
 
You said youve straight-edged the heads with less than 0.001" in ANY direction; but you didnt say if youve done the same to the decks ????? They have to be as clean and flat as the heads. 
If it has never overheated, it's unlike to have a crack anywhere in heads or block.
Never discount the possibility of corrosion or porosity in cylinder walls or decks or heads; from memory or wishful thinking (not sure which), there may be a liquid you can paint on all areas and then examine for "trail" or "spots".
Engine rebuilder/reconditioner may know better.

All back together now. One issue seems to be that the inlet gasket was correct. Or at least my new inlet gasket looked the same. As in it looks like a D not oval. I’m using a full gasket set spec’d for an oval port motor. I only have pulled down DPort motors to check with as all my other oval port work correctly. Something to be taken in that maybe. Half of the fun is in the diagnosis. The rest is trying to improve it as you go. I checked the block and it seems fine too. 6 points of reference each side and each piece. Laid the two dry together no feeler or light could be seen or go through. If my radiator leaks now I’ll fix everything with a hammer.

The inlet manifold gasket is not relevant to your issue.  I missed before that it was happening cold so unfortunately it seems you have combustion gasses in the water jacket and there is only 2 ways that can happen, by bypassing the head gasket or through a crack.  Let's hope is was just the old gasket that failed from last time it overheated. 
 
You have 160 psi compression and only 13 psi at the radiator cap and since you only have a trickle coming out the spot where the gas is getting in would be very small. 
 
I would still comp test warm (doesn't need to be hot) since even at startup the combustion chamber has experienced hundreds of explosions and the combustion chamber is hot and any small crack would be starting to open.
 
Hope it goes well.

Thanks. I’m hoping that too. I do have other heads if need be. If it fails I’ll crack test the heads and do a little more work cleaning it up.

D port Inlet Gasket needs the bottom radiused to fit the Oval Port or you will get flat spots.  Heads I tension to 85 not 60.  The engine needs to be "burped" when re-filling with water ie wait till the thermostat opens with the cap off and heater on while you fill it.  Oh and ensure a thremostat is fitted and has not dropped inside the manifold as the edge corrodes.

gtv6capri
Heads I tension to 85 not 60. 

I would be interested to hear more about where that number came from and why?

I’ve read even 90 lbs for head bolts. I cut the gasket for the oval shape inlet. The previous one was not cut and would have been restricting air flow.

Maybe for a high compression race engine with specialised bolts but that's a heck of a lot of extra tension in a standard head bolt.
 
http://www.enginebuildermag.com/2005/07/perfect-engine-sealing-starts-with-proper-head-bolt-use/

So all went back together and it’s like a domestic. If you don’t love it you’d pack up and leave but cause you do you just readjust and move on.
Started it up after adjusting valves etc and the leak was coming out the radiator as it was before just a tiny little trickle just to piss me off. I was going to install another radiator thinking the top might be bent but tried a different cap which is for a recovery system and it slowed it down. Next I pulled the thermostat and checked it (rated at 88c) it opened fine in hot water from the kettle. So before installing it again I ran the car without the thermostat and not a single drip dry as. Checked I am putting it the right way round (knew I was right but hey) spring in the inlet manifold as it should be. So I went bugger it and drilled a 6mm hole in the thermostat to aid water movement. It leaks more when cold not hot so it leaks when their is little pressure from heat. If anyone wants to enter this domestic please go ahead. The water pump is fairly new. And it’s timed nicely at about 10 degrees with timing light ( car sticker says 6 degrees) and adjusted the fuel mixture with a vacuum gauge to max and back just a bit.
I’m stumped but still love the old girl.

Does anyone know some where for parts for these prefer in Sydney or anywhere in Australia to find a full set of brass Welch plugs. All I seem to find look like zinc plated steel. Also does anyone have an original radiator they might want to part with. Thanks in advance.