A RHD conversion is not that big of an issue, the easiest is just pull the dash and cut out the firewall...then replace the firewall and all attached components: master cylinders, etc. Welding the new firewall in will be just as safe as OEM and you could add flanges and bracing to make it better than original.

As for the DA with a non-USDM 3rd gen front, I wouldn't bother...they already look similiar enough so i'd just spend that time and money on making it look or perform better.