Might still be usable after a little TLC. Like electrolytic recomposition, blasting, machining of mating surfaces, filling of "through holes," and thread inserts on the spark plugs.
Generally rusted metal objects look "worse" than they really are. Rust occupies 1-1/2 the space of the parent un-rusted metal, and the ferrous insult tends to "build on itself" making the object look much worse than it really is.
And that 1-1/2 ratio is why mechanical objects "rust together" rather than rust apart. One of my techniques as a machine restorer is to do the electrolytic bath for at least a couple of weeks before disassembly of seriously corroded machines. It makes an AMAZING difference in how easily rusty bolted connections come apart.
Interesting look at large scale electrolytic reduction/cleaning at
https://www.monitorcenter.org/counte...-of-corrosion/
Joe K