I can look at it two ways:
(1) Knowing that we won't sack Finch, I'd stick with him; relegate him to PL to show him his form is not good enough and, if he really, really wants a spot in First Grade, he needs to prove he's up for it; or
(2) Assuming we're in a world where, although we paid a bit for Finch and he has a wealth of experience, a youngster would get permanently promoted ahead of him in terms of form.
Now, if I was coach, I'd stick with option 1; I believe that an in-form Finch, in a high-pressure match scenario, could be the difference. I rate Green very highly, and would probably have him come off the bench.
But the main factor here is that, while Green's entrance into the NRL has been impressive, he's only had two weeks; if he plays next week, he could have a shocker and then go on to play badly for the rest of the season. So it's a gamble - a veteran who does have it in him, or a promising rookie who's an unknown quantity?
Long story short - if I was the coach, Marsh would be my 80-minute hooker; Riddell would be an impact running forward; and Green would be my 5/8.