After the Lions tour to New Zealand, O'Connell and Hayes have their first competitive outing which should have been at Thomond Park, but vandals put paid to that.
O'Gara and O'Callaghan saw some game time against Glasgow, but both will hope for a better outcome after the Warriors scorched home 32-10 last weekend.
The inclusion of Hayes and O'Connell means Munster will have their full Lions complement in the 24 strong squad.
Munster will be without Anthony Horgan (knee injury) and John O'Sullivan (calf muscle strain), but the good news is that Horgan's injury is not nearly as bad as first feared. He should be back inside a couple of weeks, after treatment for severe bruising.
Peter Stringer has been named in the squad but might not make it with an ankle injury.
Munster coach Declan Kidney has named four scrum halves in a back division squad of 11 players - Tomas O'Leary, Munster's Academy Player of the Season last year is named alongside Stringer, Mike Prendergast and Frank Murphy.
O'Leary, the former schools and under 21 star, figured prominently in Munster A's victory over Edinburgh on Monday and is joined in the squad by Ian Dowling, who also figured in that game, which Munster won 7-5.
Two wins and two defeats from four games leaves Llanelli Scarlets with ten points, one ahead of Munster, who have a game in hand.
Scarlets director of rugby Gareth Jenkins is only too aware of Munster's clinical demolition of the Ospreys earlier this month but says they are looking forward to this game: "We're under no illusion but we're not at all intimidated.
The appearance of Simon Easterby, the Irish flanker who made such an impact on the Lions tour to New Zealand, should add to the attendance at Musgrave Park.
: I. Dowling, J. Kelly, B. Murphy, T. Halstead, R. Henderson, R. O'Gara, P. Burke, T. O'Leary, F. Murphy, M. Prendergast, P. Stringer, F. Pucciariello, M. Horan, F. Roche, J. Hayes, F. Sheahan, J. Flannery, M. O'Driscoll, T. Hogan, D. O'Callaghan, P. O'Connell, D. Wallace, A. Foley, D. Leamy.
: L. Byrne, D. James, M. Watkins, R. King, T. Selley, M. Hercus, C. Stuart-Smith, I. Thomas, A. Gravelle, J. Davies, H. Louw, A. Jones, S. Easterby (captain), A. Popham, G. Thomas.
: D. Williams, C. Hawkins, AN Other, J. Mills, L. Davies, G. Bowen, D. Daniel.