Any good way to remove a plug thats frozen solid into a cast head?

Soak it with PPBlaster and apply heat.

If you can get an impact wrench on it, use it with proper socket,,,impact version if available and fits, recommended. Six point nevertheless for certain recommended. Should pop right out. Are they iron heads or aluminum. Use anti seize on replacement plugs

What Stump said, & I would oil it every day for several days then get after it. You NEED it to come out in one piece.

Warm the cylinder head with two large electric soldering irons like plumbers use,
and chill the lower metal section of the spark plug with either a chunk dry ice,
or the drug store Wart removal spray chillers.

Make metal temperature differences your assistant.

I once saw in the 1970s an older field representative from the Roots Blower company use metal BB's during a bearing installation. He used both hot and cold BB's . He chilled his BB's with cold blow off gas from a high pressure cylinder of CO2 gas.

Ding ding ding We (may) have a winna.

Way to much work.Saok it with a good penetrating oil. PB is like pea to me I used castle at work and now use the WD40 penetrant.Then work it back and forth easy.use a spark plug socket.at worki must have remover a few hundred that werefrozen.I used the ratchet to get them moving the used my 3/8 impact on real low to work them back and forth till they came out.Even with aluminum heads and had plugs that wer in for decades on some they came out and no damage.On my old ram charger snow plow truck the plugs were so bad that even a Snapon plug socket would not get them out.The crumbled.I finally got a metric socket on and worked them out.No damage.Rocky

You didn't mention what engine, I just spent 7 hours on a spark plug challenge on my 01 Ram with 5.9 Magnum.

without too many gory details, got the shield off, with a dremel and carbide burr , then the hex was rounded, used a tool from Grip tite, that promptly snapped off the all the spark plug except the threads that remained in the engine.
Started the engine and the ceramic blew out and I got an easy out to remove the threaded portion..

Yes,
I soaked it for 3 days in PB and Kroil... no help.

Still have 2 more to do...

Ouch!

Never mind.

got the pics of my frozen spark plug mess.

Nasty heat shields...made a real mess...

Thought I was gonna have to pull the head...

finally got it out. 7 hrs. One spark plug.

From the looks of things you may have to pull the head anyway, if it's something that you are going to run. I'm sure that there must be pieces of porcelain and junk in the cylinder.

May be able to vacuum any residue from cylinder with special vacuum attachment. Might check with a borescope from Costco or HF.

Boy am I glad I moved away from the rust belt in 1985. If I had a car like that out here I'd call the scrapper because there is no way I'd even care to mess with it.

I noticed some NGK brand ignition wires from a 4 Cylinder a few weeks ago and saw that these had bright metal heat shields attached to the silicone rubber plug boots. In my opinion that is a better design alternative than pressing the heat shields into a fit in the heads.

Was it really worth it on the Magnum V8s to use a lower quality insulation for the boots around the plug ceramic and then try to extend its working life by deflecting infra-red radiation with the pressed in metal heat shields?

I kinda suspect this was due to the 100,000 mile emissions warranty.

Yeah, the highlight of my year is buying some rust free sheetmetal from AZ or TX...

A couple of the guys in Wisconsin make monthly runs to keep our old trucks on the road.