I have been contemplating the cylinder head and have noticed
that the spark plug electrode is quite shrouded.
Given that the fire ball (flame front) is best when spherical,
the plug needs more exposure to the chamber.
So besides removing the metal around it, what would be wrong with
milling/drilling or whatever so the plug screws into the head
3 or 4 mil deeper?

You must have the wrong plugs then, most Minis now run projected nose plugs eg Champion N9Y, NGK BP6ES, or Bosch W7DC.

If you could screw plugs much further into the chamber and their threads are exposed, carbon deposits on them may prevent you screwing them back out.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Doc, I just went out to the shed to have another look.
I had two plugs laying around, a Champion N9YC and
a Bosch Super Something.
So I just tried them now in the 202 head and they are just right.
But it was the CAM 4004 head I had been looking at and they are
at least 2 mill short of the chamber.

That's because the chambers in a 998 head are smaller. The metal is there so you can grind or mill the crap out of them to make them better.

Hint: enlarge the chambers, don't sink the plugs further in...

<edit> for example here one I prepared years ago (202) it now breathes and flows better than a 295.
pic taken before polishing.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks Doc
So when it comes to porting the 4004 head, is the water jacket
smaller/same as the 202?
As you can see the "A" series is all new to me.
I was given a MG 1100 in very good condition :
and then a ute load of mini parts for almost nothing
I find this board extraordinary helpfull

Graham Russell tells me you can port a CAM4004 head out near enough the same as you can a 202. It just takes more metal removal, = more $$$.
Inlet ports are smaller and round but there is more metal thickness there. Water jacket cores are similar. He has a bunch of cut up heads there, so he would know.

I have also done 12A1456 heads off a 998 (similar to CAM 4004 but no air injection)- I stuck a 1-1/16" drill down the inlet ports for starters, fitted 1.219" inlet valves in recut seats, and blended all the ports in with a die grinder.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks Doc
The reason I'm looking at the 4004 is because of the
small ports, I'm thinkin of raising the roof of the port and
leaving the floor where it is. I think the shape would finish up a
rectangle. The idea in my head, is try a get a steeper run down
into valve. It might need a custom made intake manifold to suit.
The head would be fitted to a 1275 block that came with all the stuff.

Heads are a complcated thing but the basics are keep it simple. Its all in the flow. You would prefer not to have the end of the thread of the plug into the chamber, but level. This will also make sure the compretions are the same between cylinders

Its the Compretion, heat spots/area's and flow that matters for a head

Regarding to the spark plug gap and the plug you use. The direction the ground from the electrobe has no differance as its all ways centered anyway.
You can mark the direction, unless you want to add in heat convertion and ground of earth of plug and chamber of head

I have no experiance in moding headds, but

This is the way I see it,

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Stop Licking the Dog...I Don't Care Who Started It

I would not try and use a smallbore head on a 1275 block. Some of the gasket holes in the head won't seal with a 1275 gasket, and ports are way too small, valves too.
Get a 1275 head and work that.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

So true...so true... but that's why we like to play and experiment
with them, kinda like a woman, eh...

So would the 4004 go on a 1100?

dont go thier Head we can give to some one to work out for us, but a woman they are all differant, to find a leak you can fix it...so maybe its not quote the same but yes you have to make it happy

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Stop Licking the Dog...I Don't Care Who Started It

Yes a 4004 will run fine on an 1100, but the stock inlet valves and ports are a bit small. But torque is good.
A 202 is better for power....

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.