I've prepared four new Heroes (complete with miniatures, hero cards and deck cards) for use with virtually any Hero Quest stories out there.
Obviously if your quest requires that a certain Hero class has to use a certain artifact, some tinkering would be necessary there, but otherwise they should work.
I've been play testing them with a group of semi-regular players on the Japanese Game System (using the NA rules, no solo adventures yet). So far, so good. The first character to "really die" perished shortly before we found the Talisman of Life, so it's cool. I am starting to wonder if the Mystic is somewhat over powered while the Cleric and Ranger might be slightly under powered. But I'm okay with some characters being meant for support, and different playing styles.
My Mystic is a female Wizard type with fewer spells and spell choice but more flexibility in terms of weapon usage (can use up to a broadsword, but no bows). I created a new deck of 8 spells (culled from the unused ones from Legacy of Sorasil pc game), and she may pick up to 5, exclusive to this class.
My Ranger starts with a bow (2 attack), gets +1 movement and has same armor restrictions as Wizard. He can disarm traps with SHIELDS (same as a Tool-Kit), and has special ability to once per quest either detect a trap on the other side of an open door OR detect traps & secret doors in the room/corridor with monsters present. Weak BP.
My Paladin starts with armor (chain mail) and gets +1 movement if he wears plate. Starts with 1 Holy Water (heals 1 MP if used on a hero or 4 BP damage vs Undead) for each new quest, and he gets "Holy Flame" (inspired by Japanese GS rules) which rolls 2 attack dice vs dice equal to enemy's MP (undead can't defend).
The Cleric is similar to the Paladin (starts with a cloak as armor), but starts with two healing abilities: one heals up to 8 BP (divided among any allies you can see at your discretion), if used to heal yourself it only restores 1; the other only heals yourself (roll 4 white dice and restore 1 BP for each white shield... the first time it was used by someone to save from death, they failed to roll any!). This character is restricted from using edged weapons (I created "blunt" equivalents that cost more; bows aren't restricted). So while she can't use a shortsword, she can wield a mace. Instead of a hand axe or battle axe, she can purchase a hammer or (huge) war hammer.
The "Abilities" or "Skills" of these characters function exactly as magic spells, while the Paladin's Holy Water can be stockpiled like a potion card (in theory, he could give it to another Hero to use).
The last three characters have both male and female versions that are identical other than appearance. I also expanded the armory to add new stuff for everyone. The Cleric starts with a Cloak and Mace, the Ranger gets a short bow (2 attack dice) but fights with a dagger (1 die) close range. Many more items were added but most of them the Heroes can't afford yet (using the NA rules you don't get money for each monster kill... but I will be honoring the "all your money to the temple to resurrect one time" rule, if needed).
So for the Japanese campaign I'm going to do it like this:
Modified Frost Bow to be usable by an Elf OR Ranger.
Modified Silver Sword to be usable by a Barbarian OR Paladin.
Modified the Rod of Memory to be usable by a Wizard OR Mystic.
Modified the Flame Axe into a Flame Hammer to be used by a Cleric (identical usage)
We are currently beginning Quest 4. I may have made Quest 3 ramp up in difficulty a bit too much though. I didn't add any new monsters but did make it so that once the "alarm" sounds, the monsters attack with black dice and defend with blue dice (except when defending against magic).

But ultimately I just want to have these characters available so that, in theory, we can start up a quest any time with a group of Heroes, using any mix, even with more than four (though, having the Mystic and Wizard together might be a bit too easy, a bit like having two Barbarians at once, but I could always make the campaign harder in other ways).

I also came up with a basic leveling system (based on number of quests completed) I will post on here in more detail eventually. No telling on its effects, but I mainly was thinking of it to ease the new "weaker" characters up a bit to get them ready for the really hard quest packs (BQP & EQP).