Maybe either a 4-3w-1-2, 4-3w-2n-1 (X-Mas Tree).
For stuff other than formation:
If possible max all bonuses (morale, condition and win bonus). Being a KO round matchup, opposing managers tend to invest more (if they can) in these matches, compared to a mundane league match.
Do you have any players that have been in poor form or does he have players with extraordinary form, that could result in the narrow diamond being less effective than normal in this matchup?