All you can do is ask. You can't tell what someone will do until you try.
That's what it sounds like to me. Marek's doesn't hit that fast, it takes time for the lesions that cause the damage to grow.
Golden Comets are not a breed, it's a marketing name often used for some red sex links. If they are reddish you got a girl. If they are white/yellow you got a boy. There are two types of Golden Comets. Some are based on the commercial egg-laying hybrids. These are the ones with with the more likely health problems. Not guaranteed health problems but more likely. The other type are what you get when you cross two regular breeds, maybe a Buff Orpington or New Hampshire rooster over a Delaware, Light Sussex, or certain White Rock hens. There are a lot of other breeds you can use. These are no different from any other dual purpose chicken.
These different marketing names cause a lot of confusion and worry on here. You may think they are breeds but they are not. They can have different traits depending in who is using which marketing name. I agree with Mrs. K, enjoy them and give them a decent life. That's the best you can do. It's hard to do any better than your best.