There is 4 13mm bolts at the back on either side of the alloy part of the tray and 2 at the front tucked up behind the bumper pointing upwards the plastic should come with the alloy cradle
If it was mine i would be putting a New timing belt on the new engine and possibly a clutch and maybe putting a head gasket on it at the same time as 50k seems to be the rough mileage they go