UPDATE - 7 NOVEMBER
So it turns out you can transfer money from SL to InWorldz. And that Redgrave have a skin store in InWorldz. Thus ends my period of definitely-not-going-to-spend-any-money-on-my-avatar-this-timeness. I knew it wouldn't be long.
One purchase later, and InHuck is looking pretty much identical to SLHuck.
Except for one detail... a freakishly pointy chin...
It's a measure-by-measure copy of my bespoke SL shape I'm wearing (by Scarlett Rhea of Harlot, incidentally), so I'm assuming this to be some sort of InWorldz quirk.