On paper Boston should get easily beaten by Kidderminster, having already lost both home and away against them in the league. However in the FA Trophy Boston won 4-1 just a week after losing the league game 1-2. So anything could happen.
My Computer reckons a straightforward Home Win I'm going for:
Kidderminster Harriers 1-1 Boston United (2400)
As is usual with such knockout games decided on the day by extra time and penalties if needed, the prediction is for the score at the end of normal time.