1. It's your tank, so don't take the opinions unless you want them. Just facts.
2. They can live in 70's based on reef keeping history/testing.
3. Just think though that's the MINIMUM tank size. the minimum for clowns is a 20G I think, idk if you've ever seen a FULLY grown clown but they're pretty big 4 inches about. I've seen some 4 1/2, so would a pair of 4 1/2 inch clowns be completely satisfied in a 20G? Who knows, we can't read fish minds, do they seem to be okay and not too aggressive. yeah.
Same with One Spots, at 70G They seems to not get aggressive.
When a fish has
definitely not enough space they start attacking other tank mates.
So just realize by keeping them in the minimum size tank, you eventually could possibly have a problem on your hands.
Will you? We don't know.
chances? probably 20%?
Less with a bigger tank, of course. more with a smaller yes

. Some people seem to think smaller tanks will stunt growth to keep them "adjusted to your tank size longer". Idk if there's science behind that, but I've seen fish out grow tanks all the time so IDK how that works.
If you like it, and you have a 70G I'd say do it. But be ready to care for your fish all the way through. I and many others have kept juvi fish as well in smaller tanks until they grow.
You can always put a fish trap in, capture him, and bring him to your LFS as a donation, in order to save lives, and make happy fish.
If you enjoy him for 6 months to 2 years in the meantime, worth $80 to me. But then again, you have to give up your pet, or then upgrade. so not necessarily just about the money. Also about the heart.
It's just a big risk man. So up to you.