Peacock had been out since August when he suffered a ruptured cruciate ligament against the Tigers.
But he showed no hesitation in returning to the fray just four days after McGuire had made his first appearance of the season following a seven-month lay-off.
The pair’s return comes as welcome relief to Brian McDermott, who can now sleep easier after a run of three successive wins over Easter.
McDermott said: “They’re both very influential people but I reckon it will be another three or four weeks before we see the true Peacock and McGuire.2
Despite the one-sided final score, it was Castleford who largely dominated the first half.
However, through misfortune and their own errors, they somehow trailed 12-0 at the break.
In between, Jamie Jones-Buchanan had crossed from McGuire’s pass to claim Leeds’ second touchdown.
McDermott added: “When it mattered tonight, we came up with the plays.
“Had Castleford scored (early on) then the game would have taken a different look. They would have grown another leg, and who knows what could have happened.”
The visitors had got off to the perfect start when Kallum Watkins squeezed over just 90 seconds after kick off.
Then their combination of defensive grit and clinical finishing kept them ahead despite the hosts piling forward.
Castleford were still in with a chance after 50 minutes, but Leeds suddenly burst into life.
Tigers boss Terry Matterson said: “It’s been a tough seven days for us and it’s just been a game too far.
“It was a really good start and a couple of tries got taken away from us. Emotionally it got tough at the end.
“I was disappointed with the last 10 minutes because we’ve fought to the death in every game, but today we let it go.
“It’s just not bouncing our way at the moment, and Leeds can do that to you. Once they get on your throat they go for the jugular.”