Rust has way to much talent to be on the 4th line man. I'm not even gonna get into Riley as the 3C.

Sheahan fits a 3rd line C role better than brassard but playing brass on the wing doesn't make sense. Sheahan will be the 3rd C when brass leaves next year

Few things:

IDK about playing Brassard on the wing
Rust shouldn't be on the 4th line, maybe put him at 3LW instead
Guentzel, Crosby, Hornqvist was the pens best line in the playoffs, why not keep it together and put Sprong on Malkin's line instead?

Sheahan will not be a 3C here. If they saw him as a 3C they wouldn't have traded for Brass putting a huge hole in their defense in the middle of a cup run.
Sheahan is a prototypical 4C. He's big, he plays a physical game, he's a grinder. He does not fit the role of a push the puck, up tempo game that the pens want to play on 3 lines.

See that right there is really the thing.
Kessel and Malkin tore it up, so why would you separate that? I know the coach likes to spread the talent on 3 lines. Blah blah that's just a mess. You named the 1st line, the second line to me frankly is obvious.
Sprong's right position is on that 3rd line, with Brass and Rust, two responsible players to help him get the D down and let him use his skill down there to really give that line a kick.

when they traded for brassard , Sheahan was performing good. and even after they got brassard he still played better than him. why do you think Sheahan played 3rd line most of the time & took most of the key faceoffs in the playoffs? because he was playing better. brassard doesn't even kill penalties nor is he good on faceoffs like a 3rd line C should be . Therefor Sheahan will be the 3rd line center next year, Certainly won't be a rookie like Blueger or Bellerive at 3C next year

& Sheahan is not a "grinder" nor does he play an overly physical game. if anything he should be more physical. he's a Two Way forward who can take key faceoffs and kill penalties. just like bonino.

The pens will be looking for a 3C next year.
Sheahan isn't the answer. The styles don't match what they want to do. They brought him in last year to be the 4C. If they thought he was the answer you wouldn't have brass now.
Brass came in and was instantly put in the 3C spot. That should tell you all you need to know.
I agree Riley's play was good last year, but it's hard to really judge with Brass having a groin injury. He plays a faster game than Riley. That's what the Pens are looking for in that role. My guess is Riley may find 3C work somewhere if he plays well this year, but it won't be with the Pens. They see him as the 4th line center.

He is a grinder. His game is on the boards. Come on man, at least watch him play.

Could you imagine how much of a defensive liability that line would be of kessel malkin sprong?