[V10 2nd Gen]

My truck is nearing 174,000 miles, which is my next service interval. The truck has been serviced at 3000 miles, all 3 owners, myself included, have done it this way. The previous owner changed the plugs at 100,000 miles, shortly after he bought the truck. The original owner changed them at 50,000 miles. I am 3rd owner. The 2nd owner put 100,000 mile plugs in, I know him on a personal level, he said I ought to change them at around 175,000 miles, 75,000 miles from when they were changed last. So I intend to replace them next oil change, like I said, at 174,000 miles.

What material of plug should I use?

Should I replace my injectors? They are getting up there in mileage. Form what I've read I'd need to take the intake manifold off, requiring a new gasket set for that. Bosch quad-port injectors, set of 10, retail for ~$200. Gasket kit is $35, plugs are about the same price as the gasket kit.

Anything else I should do?

 

[69 XS29L]

The debate on plugs is endless and moronic. All opinion no data. If your plugs ran 75k then why not put the same type plugs back in. I run an upgraded Davis ignition and Bosch Platinums on my V10. Some folks claim Magnums will only run on copper plugs. Whatever.
I like the idea of preventative work, but be aware, while lifting the upper intake is fairly straightforward, the vacuum lines at the back and all wiring under the hood can be a brittle can of potential worms in high heat areas. Especially the injector plugs for whatever reason.
If you have the early style plastic thermostat housing and it does not leak, don't touch it if you don't have to. Upgraded non-leaking cast aluminum ones are scrapyard only.