Not to knock the aussies ( never tried them ) there is a us supplier with similar gaskets: Remflex. Side note: If the manifold surfaces aren't matched up, even a 1 inch gasket aint gonna help, don't ask :)
I'm no help on the engine build but for the A/C system, give Charrlie_S a PM and have a chat ( knows his stuff, super nice guy, mopar fan, nuff said )