Sea-Cock type?

Wilcox Crittenden. You can see the WC logo near the base of the casting.

That’s what Hatteras used as well back then. I replaced them all with new.

Wilcox Crittenden
I serviced the cocks to my mains. Slowly been replacing all others.

Old bronze. Never a hammer, Mallet or hammer and block of wood.

I rebuilt a set of those years ago, breaking them down and lapping them in with valve grinding compound. They were beautiful when I was done and operated very smoothly when adjusted just so. Unfortunately, the sweet spot of turning easily and not leaking is completely elusive. Ultimately, getting them to turn required Ralph's persuasion method. Be careful with the "Love Taps", because the stud with the nut is very soft and bends very easily. The things should be replaced so that anyone can swing the valves and save the boat if ever necessary without finding tools and employing a multi-step process. The only good things that can be said for them is that they can turn in either direction and the handle can be positioned in 4 directions. That and they can be polished up to make a shiny table lamp base

Electrolysis, galvanic erosion, corrosion, old age; what ever it's called turns that old bronze into a fragile device.
When I replaced many on my '78 Bert I learned one good rap with a hammer could smash a cock or thru hull like ice.
Bertram used bronze machine screws thru the hull, thru the backing board to the cock flange. A hit on the cock would break the screws.
Other times they would deform like putty.
WCs and some Chinese copys use a nut to make tension on the tapered insert. A solid face strike here can damage or break the threaded parts
Also deform the taper or housing loosing the near perfect fit.

Been messing around bilges for a while now.
When trying to close cocks on other boats, I have felt something start to deform. I stop before they break apart.

I have witnessed the aftermath of people leaning to hard on a sea cock. AND beating on them.
Those handle extenders scare me also.

IMO, there is not much in a bilge that requires a hammer.
Correct installation, maintance, care and yearly operation of sea cocks removes any need for even that block of wood.

It's the lapping compound that saved my big WC engine sea cocks, like the OPs. Lots of water proof grease makes the final sealant.

There have been times when I also wondered "Why and I replacing this solid PIA thru hull" .
I believe Murphy hides in my back pocket at times.

Think it's the 5200 curse some times when removing thru hull parts. 5200 takes a hammer blows and laughs back.
I often wander if I could make a tank of that stuff. Shells would just bounce off.

Bottom line for me, treat it like ice or ice cream when it's it the water. I've never accidentally flooded a boat yet.