So I came up with a 3rd method; redrawing the layout so that all of the early stages are represented on just one game board, before the Heroes find a single exit that leads to the next game board (which has the next stages), and so on. In other words, making it more like a traditional quest pack, but keeping the concept of no recovery of health & spells. I wanted it to match the original as close as possible, with the only real difference being not having the doorways at the edges of the game board.
A quick drawing of how the 13 stages link together in the official quest showed that it was indeed doable. This drawing is shown below, with each dot coloured the same way as the stage in the quest book, with the size of the dot approximately representing the size of the stage (number of rooms etc). I figured I could group the stages together using the dotted lines shown below, with each grouping representing one 'dungeon level'. If the Heroes were tough enough they could battle their way all the way to dungeon level 4, and the final showdown with Hinsgrim, the boss of the Dark Company.
Below you can see Dungeon level one. It was a little bit of a squeeze, which was not surprising as it has the most stages crammed into it, but it worked even better than I hoped. I only had to eliminate a few empty rooms, combine a couple of rooms into a single room, and change the flow a little bit, and it checked out. Crucially, it has the same number of monsters as in the official map, and uses the doors and furniture available in just one Heroquest set.
The quest notes are below. DW on the map stands for Dark Warrior.
A - The Heroes begin the adventure on this stair tile. They must find another stair tile in order to progress to Dungeon level 2.
B - This secret door may be opened by the Evil Wizard player on his turn. The monsters in the room are placed on the game board and may move and attack.
C - The closed door here separates the corridor into two sections. Once opened, remove the door from the game board.
D - The treasure chest contains two hand axes.
E - This chest contains 50 gold coins.
F - Any character stepping into this room will notice how warm it is. If he finishes his turn standing in this room he must roll one die. If he rolls equal to or greater than his mind points, he falls into a wasting sleep and loses one body point. On his next and subsequent turn, he must attempt to roll equal to, or less than his mind points on one die or remain asleep and lose another body point. If he does awake, he may take his turn in the normal way.
G - A Hero searching for treasure in this room will find a magic scroll of spells. If the Elf or Wizard find this they may choose to miss one turn and read the scroll. Once the scroll has been read, it disappears. The reader may then regain all the spells he had at the beginning of the adventure.
H - A Hero searching for treasure will find a crossbow on the weapons rack. However, there are only 6 quarrels. Each time the player fires the crossbow, mark of one quarrel on his character sheet. If he runs out of quarrels the crossbow cannot be used again until he finds some more.
I - This treasure chest contains a potion of healing which will restore up to four lost body points.
J - This is the exit to the next dungeon level (level 2).
K - This is a Shrine of Learning. Once all the monsters in the room have been defeated, the Elf or the Wizard can attempt to build a full complement of spells through meditation. The player rolls one die on his turn. If he rolls equal to or less than his mind points tally, he can regain all the spells he had at the start of the adventure. If he rolls a greater number, he is gripped by a magical vortex and loses one body point.
Wandering Monster: Dark Warrior
Dungeon Level 2 to follow shortly...
fraggle yeah! 
You guys rock!