Just look for HQ-WB ute, van or cab-chassis rails and cut what you need out.
For rusted body mount holes best bet is to buy some big flat washers with the same size hole, cut out a piece the size of the washer OD and weld the washer in in. On a tonner I had once I just welded the washers on top of the chassis. It raised the body 3mm but I just stuck the same washers under the radiator support mounts and all worked.