The decision is shaping as a key factor in the game plan the Giants will take into Saturday night's must-win semi-final against West Coast at Spotless Stadium.

The Giants are tossing up between handing Rory Lobb the No.1 ruck role he covets or promoting big man Dawson Simpson from the reserves to take on the Eagles' pairing of Nathan Vardy and Drew Petrie.

Simpson's selection would allow the Giants to maintain a taller forward line, which has been a feature of the side in the past two years but has come under intense scrutiny in the second half of the season.

If Lobb was shifted into the ruck, Jonathon Patton and youngster Harry Himmelberg would be the likely main targets in attack, with Toby Greene, Brett Deledio, Devon Smith, Matt de Boer and perhaps Steve Johnson rounding out a more mobile forward line that would be better equipped to lay defensive pressure.

It would discourage the Giants from bombing the ball into their forward line, which would play into the hands of West Coast's Jeremy McGovern, who is one of the best intercept marks in the game.

Richmond's mosquito fleet set-up in the forward line had been seen as a weakness, but has turned out to be their strength in their stellar season.

"It's a tough one. We have to work out what is best, not just for the rucks but the team," the Giants ruck coach Dean Brogan said.

"There's a bit of 'do we go really small or try and stretch West Coast with our height and back our talls?' I like either ... these are the discussions we'll have over the next 48 hours."

Lobb, who is the club's long-term ruckman, was one of the revelations of 2016 but his form graph has plateaued this year due to injury. One of the best contested marks in the game, Lobb's aerial prowess would be magnified competing against a ruckman rather than a key defender.

"Because of Mummy's dominance and ability to hold the spot for a long period of time, Rory's chomping at the bit to get the position when it arrives," Brogan said. "If it's Saturday night or the year after I think we have some time up the sleeve.

"He's had an indifferent sort of year with his body compared to last year, but given an opportunity he'd grab it with both hands."

???

Simpson has filled in twice for Mumford this year, each time pleasing the Giants' coaches with his performances.

"He's a genuine ruckman - old-school, big body, jumps in hard, gets to contests," Brogan, who played in Port Adelaide's flag in 2004, said. "He organises the mids really well. The boys love playing with him. He's a really good character to have. He has that old-school from 10 years ago when they were big, told the mids where to go, scream at you. He's a really imposing figure."