Loosehead McGrath (24) played three times during November's GUINNESS Series, crowning his debut with a man-of-the-match display against Samoa.
The pair are now pushing Ireland regulars Cian Healy and Mike Ross for their scrum spots, while another Leinster front rower - hooker Sean Cronin - comes into the Championship in excellent shape after making six starts in the Heineken Cup pool stages.
The 27-year-old Cronin has 30 Ireland caps to his name, the last of which was an impressive 65-minute performance against New Zealand in November.
Speaking about Ireland's reinforced front row ranks, Rory Best said: "I think it obviously brings competition for places which is good for everyone. When you are training it puts pressure on because there are some real quality players there now.
"So, whenever you are training, if you don't get it right in the scrum, you are going to get done. It closely replicates this weekend.
"That type of thing is great to see. Especially with their age profile. These guys are young. They have got a fantastic future ahead of them but it is important now they know this is just a step up.
"Getting into the extended squad is step one and the next thing is getting into the matchday squad. Then you've got to be looking to start and looking to push on and better yourself every time. With the attitude these boys have, that is the attitude they are going to adapt.
"They will give you that impression. It is great for the squad. Ultimately you need to be able to bank against injuries but competition for places drives everyone on and it's a good thing."
Scotland's interim head coach Scott Johnson has made four changes for the trip to Dublin, and Best knows the sort of trouble the visitors can cause - especially after last year's 12-8 defeat at Murrayfield.
Not only do the Scots possess a very physical pack but they have two 2013 Lions in their back-line in Stuart Hogg and Sean Maitland.
Commenting on the selected Scottish team, the Ulster hooker admitted: "I suppose it is not far off from what we expected. There are a couple of tight calls in there but we know them quite well from playing PRO12 against them.
"It's a strong team. Their back row especially are very abrasive. They have a strong front five, so from a forwards points of view it is never easy playing Scotland.
"And with the team they have picked and the pack of forwards they picked, it is going to be very much a case of rolling up the sleeves and preparing for battle on Sunday.
"We talked about their backrow but also with Jim Hamilton and some of their front row, they are very, very dangerous over the ball if you let them get in.
"It's going to be very tough to slow their ball down. They are big men, they carry hard and they are phsyical around there. It is a great challenge."
Ireland's lineout had been questioned after some disappointing displays in last year's Six Nations, but rather than focus on the lineout winning ability of opposition lock Hamilton, Best feels Ireland need to focus on their own capabilities and that of captain Paul O'Connell.
"They did fairly well against us last year at Murrayfield and he (Hamilton) is a good lineout operator, but we have Paulie (O'Connell) there now who is a brilliant lineout operator.
"We need to make sure when they are moving around and getting up we are accurate. That is throw, lift, catch. Eveyrthing needs to be right and on the money.
"Scotland are a team that are going to test you in the lineout. It's called a Test match for a reason. It is to test yourself against the best and Scotland are up there."
November's narrow defeat to the All Blacks was felt even harder by Best who fractured his right arm during the first half of the game.
But he states that the Irish squad have parked that loss - as well as the previous reversal to Australia - and hope to build on the positives during the 2014 Championship.
"As players, in the Australia game we got the balance wrong. We were so preoccupied with knowing our plays, knowing our roles, getting the drills right," remarked the 31-year-old.
"We didn't play with the emotion you would expect in an Irish jersey. That was something we corrected in the New Zealand game.
"Now, with having this two-week preparation, it has been good that hopefully by the time we leave the training, it will come automatically to us - our roles within each play - and we can concentrate on building up and bringing physicality to the game this weekend.
"We talked about it (the defeat to New Zealand) in the Christmas camp. We looked at the last three minutes where we lost it.
"We looked at some of the positives that got us into the lead and also looked at some of the negatives that allowed them to come back at us.
"At Christmas as far as we were concenred it was parked. We need to, as a bare minimum, reproduce the same positives that we had in that game and try to better them."