flathead 6

[Bill Davis]

I will add this to what Go said - make sure you blow off or sweep off the cylinder head around the spark plugs before changing the plugs, since the plugs are sitting in a bit of a well.  You do NOT want any foreign matter falling into the cylinders.

[Go Fleiter]

Hallo + welcome!

You should use appropriate Spark plugs.
Then, You must check the clearance to be 0,035 inch.
If You don´t have: You need a Service Manual!
You get Plugs  for Your engine (and Manual reprints!) for example here, very competent people:

https://www.oldmoparts.com/

Edit: found my plug list:
They sent me these (since) until now:  AC43-5, NGK B6s,  Blue Crown M.
I faced some broken porcelain bodies of Champions.
While possibly beeing singular incidents, I don´t buy these any more.

For sure there are lots of other shops.

Greetings from Düsseldorf!
Go

[Tee Jay]

I own a 1952 ply Cambridge 6cyl. the car is in totally 100% original condition, excepting tires on the ground. It run's like a car should with 32,000 miles. Recently I have begun to notice a slight miss. In considering a spark plug change, what precautions should I take? The plugs have been in the heads for 71 yrs?