Being more of a woodworker than metal worker for 64 years, I can speak with some experience.There are at least as many opinions about wood finishing as there are about which motor oil to use.
If the wood is still in good condition, you probably don't really need to do anything. After all, it has held up for 50-60 years with nothing but the factory finish. If the parts are not exposed to sunlight, there is no need for UV protection.
That said, a coat of polyurethane varnish certainly won't hurt and may help preserve your wood.