Easy, just use a 4spd 308 block and leave the aussie 4spd where it is. You have the same issues with speed sensor as the trimatic, need a short speedo cable with a fitting on the end that replicates the threaded fitting on the TH boxes. Then put an inline speed sensor on it, and then a HQ Muncie speedo cable from there on. Not sure why you'd want to use an aussie 4spd though when you could have a 4L60E, which requires no body mods other than to drill the TH400 speedo cable hole in the firewall?? You could use a T5 but it gets very expensive finding the right box, bellhousing, tailshaft mods etc. You'll be up around $3500 or more by the time you get it all. Of course you could use a Muncie or cr@ppy old toploader but both normally need minor surgery on the tunnel.