Campaign Plan Changes

I've been slowly putting together a sandbox-ish campaign for The Hero's Journey.  Slow going chiefly because of my large capacity for self-doubt.  However, it all may be a moot.  I introduced one of my co-workers to Beyond the Wall.  We spent a lunch hour making two characters and a village.  She loved the playbooks.  I mean loved them.  And really liked creating the village too.  I lent her the rule book and she took it home and went through the character creation process with her husband.  He really enjoyed it.  He's big into world building so he particularly like building the village.  She likes the magic system too.  She really wants to play Beyond the Wall and experience character/village creation with a larger group.  Since she is kind of the key to the nascent group, I believe we will be using Beyond the Wall for the campaign.  I made sure that she was cool with ultimately having only three actual classes.  After all, she was the one excited to play an acrobat and looked forward to founding a carnival.  And, since I have Further Afield, after the first adventure we will be making a shared sandbox for the setting so at least some of the setting pressure will be lifted.

My only have two hangups with this.  The first is that I really like The Hero's Journey and Swords & Wizardry Whitebox as a rule-sets.  I like that you essentially just use d6s and d20s.  I like the unified savings-throw.  So I'm thinking I will somewhat hybridize Beyond the Wall.  Beyond the Wall and The Hero's Journey/ S&W WB are not too different so it shouldn't be too hard even for me.  Beyond the Wall only lists 10 levels so I will stick with that.  It also has ascending AC and a To Hit Bonus system, which is my preference.  It will be easy enough to unify the savings-throw.  But classes have different hit-dice and weapons do different dice damage.

So, it's advice asking time.  With BtW having different hit dice for each class, should I stick with BtW rules-as-written?  Or should I use THJ/WB stats?  Weapons do variable dice damage so changing that depends on the hit-dice used.  Or vice-versa.  I've really been wanting to try The Hero's Journey rules for armor damage reduction value.  That's one of my favorite parts along with the increase in the utility of the shield when it comes to armor class.  So should I fold that in?

My second hangup is whether or not I have the improvisation shills to handle a setting not completely in my control but unless someone has advice about that I'll have to deal with it on my own.

Oh, I guess I should ask.  Has anyone mashed up THJ/WB and BtW?