Creative financing

I'm holding my breath for a miracle here - someone is coming from way west of Ceduna to have a look at my house and are making noises about cash sales and sharing conveyancers, so they're pretty serious.

I need a lo-doc 60 for a $100k transportable. If this house sells, I have around $55k cash downpayment and $50k equity in land and another $100k equity in another house. Because its a transportable I can't get finance for the place until *after* it is finished, so if my old house sells (counting my chickens before they are hatched here) I should just need to pull $45k equity from my current house to pay the balance.

How the hell do you structure this kind of thing? It would leave me with an IP with around $130k owing on it (its worth around $190k which goes over 60% so this is stretching it, but lets not split hairs), of which only $55k is actually for that IP and the rest is for the new PPoR. And the PPoR will be totally unencumbered and not used as security against anything, unless the bank has snagged the title for the land the PPoR will be on and used it as security without telling me - can they even do that?

Would I be best to get another loan for $75k secured against the PPoR after everything is through and pay off the non-deductable part of the IP, or what?