Copper head gaskets can be made to specification, and can even be reusable. I've had good success in the past trying to sort out vintage engines For example.
https://www.coppergaskets.com.au/
I probably have a bare head in my stash, but I am far from local. Let me know if you can't get something.
It can also be worthwhile dulling the sharp edges in the chamber so that they are slightly rounded. A scraper or jewelers file followed by some emry works.
Have you had the distributor to bits? The little plastic lugs at the connection posts to the springs break, as does the washer under the weights . The weights and the advance is all wrong, and they tend to cause lots of pre ignition once they have got out of whack here. Also the old grease on the shaft gets hard.
