The two clubs are locked in a three-way battle with Manchester City for the last Champions League place in the Premier League and failing that the title of best of the rest.
Bilic's East London revolution has been spectacular and the club could be even higher up the league had they not suffered a glut of long-term injuries to seven key first team players all at the same time in November.
Indeed even in the last three weeks had they not suffered at the hands of some poor refereeing decisions, the Hammers could well be six points better off.
Bilic's side have surrendered leads in 2-2 draws with Chelsea and Crystal Palace and then 3-3 with Arsenal last time out with a number of decisions going against them.
So what changes does West Ham's popular manager need to make to the side that started against Arsenal in order to seal a place at Wembley on Wednesday night?
Randolph in for Adrian
Darren Randolph has played all of West Ham's cup games this season and impressed every time.
In fact Adrian's recent poor form makes this an even easier decision for Bilic, who has already confirmed Randolph will play in the historic game.
The Republic of Ireland hero has been superb when called upon in West Ham's tough cup run so far and will relish the opportunity to stake his claim for some Premier League minutes when he faces the Red Devils at Upton Park.
Collins in for Reid
Winston Reid is arguably West Ham's best defender but he has been out of form since his return to the side after his latest injury lay-off.
In 19 games together at the heart of the Hammers defence, Reid and Ogbonna have conceded 29 goals. In the 11 games James Collins has played alongside Ogbonna West Ham have conceded just eight goals.
Bilic's side have missed in-form Collins' determination to hold on to leads and all round experience in recent weeks and his return to fitness comes just at the right time as Reid clearly could do with a rest.
Obiang in for Tomkins
James Tomkins looked rusty against Arsenal on his return from injury last time out and was replaced at half-time with Michail Antonio deployed as a right wing-back.
With Andy Carroll starting up front again Bilic should look to use a similar tactic and will need Obiang's class on the ball and the extra protection he provides in front of the back four too.
Hammers fans are big admirers of Obiang but he has been sparingly used this season. But everytime he plays West Ham tend to win.