Willie Faloon and Eoin McKeon complete the all-new back row, replacing Johnny O'Connor and George Naoupu respectively.
Brett Wilkinson will start in the loosehead prop position, while new signing Nathan White gets his first start for the westerners at tighthead prop.
Elsewhere, in the back-line, the fit-again David McSharry has been drafted in to reform his centre partnership with Eoin Griffin - he replaces Mata Fifita.
The Scarlets are riding high after two successive wins and are perched proudly at the top of the league table.
Connacht boss Elwood was very pleased with his team's performance in Parma last weekend and the 30-17 win over Zebre, but he knows there is a lot of work to do if they are to overcome the Welsh region.
"We played well against Zebre, scoring three tries away from home and securing our first win of the season," he said.
"The lads showed huge character in Italy, especially when we were forced into making so many changes in the second half. Tomorrow poses another challenge as the Scarlets are top of the league and are playing very well.
"They've had a great start to the season, scoring 10 tries in the process. We will really have to step it up against this Scarlets side but the lads are well up for the challenge."
CONNACHT (v Scarlets): Gavin Duffy (capt); Tiernan O'Halloran, Eoin Griffin, David McSharry, Fetu'u Vainikolo; Miah Nikora, Kieran Marmion; Brett Wilkinson, Ethienne Reynecke, Nathan White, Michael Swift, Mike McCarthy, Andrew Browne, Willie Faloon, Eoin McKeon.
Replacements: Adrian Flavin, Denis Buckley, Rodney Ah You, David Gannon, Johnny O'Connor, David Moore, Matthew Jarvis, Robbie Henshaw.