Navigator valve seat hardening

Should be Austenitic cast iron and therefore no issues with unleaded. 

Unleaded has been here for 45 years now and it really isn't a reliability issue. 

Just fit and forget to worry about it.

George 

It's only iron heads that have issues with unleaded unless they have new seats, alloy heads had the hardened seats from the factory regardless of what some head reconditioners say.

... are OK unless really hard worked. The FBHVC did some tests years ago withan A series BMC if I remember correctly.

Your Jubilee, Navigator & Electra valve seats are perfectly sound & do not need anything doing to them. As stated above, they are made from Austenitic steel and work harden.

As for Cast Iron cylinder heads, the example I heard was if you towed a caravan with a Cortina, Sierra or Granada flat out for over a 100 miles, you might just notice some valve seat recession.