withal > also, in addition

2 That nothing, seemed, might bear so monstrous might:

That > [So that] seemed > [it seemed] so > such

3 The one upon his covered shield did fall, 4 And, glancing down, would not its owner bite: 5 But the other did upon his truncheon smite,

truncheon > broken lance

6 Which, hewing quite asunder, further way 7 It made, and on his acton did light,

acton > {Stuffed jerkin worn under chain-mail; later, a leather jacket covered with chain-mail} light > strike; fall, alight

8 Which dividing with importune sway,

importune sway > grievous force

9 It seized in his right side, and there the dint did stay.