I purchased a replacement chassis for $ 24 and modified it to fit the Commodore.
Chassis has to have some trimmed off the front as well as the rear. This is shown in the pictures below. The rear mount posts have to be shortened to get the right body height. The front mounts are too short so I used the styrene in layers until the body was resting on the styrene. thread . with the body in the correct position I drilled through the body mount posts into the Styrene. I used a 1mm drill into the styrene . I used a body screw with a sharp point cut the thread in the styrene. Once the body was the correct height & position on the Chassis
A Ninco deep wood guide can be fitted but the post hole should be bushed as it is too big for the Ninco guide. A bit of the rear top of the blade needs to be removed to clear the chassis. I used Brass tubing as a bush for the guide post and glued it in. A Scalextric deep guide could also be used but check it does not lift the front wheels off the track. Also add awasher over the post to make sure the gide does not drop to far and passes the guide stops.
The front mount ready to drill holes for the Ford chassis post location. The Holden body posts are used to mount the styrene plate . The ford chassis screws locate where the white plastic wall plugs are located.
The M2 (2.2mm) fine thread screw by slot .it are best to mount the body. The body should move very freely on the chassis . The fine thread screws are less likely to unscrew in service and have a blank section which allows free body movement.
All body screws should be covered to prevent them dropping on the track if the do come loose.
The rear of the chassis in the top picture . The "corners" have to be removed do the body fits inside the rear of the body. Also some has to be taken off the rear edge of the chassis.
In the lower picture the front of the chassis was trimmed and beveled off at the top edge. The front sits under the spoiler of the body.
The Commodore body is heavier than the Ford FG . It does need some work on the weight distribution to get the best handling . The car is prone to tipping out of the slot when driven in anger. The FG Ford does this as well but not quite as much as the Commodore. I spent a lot of time trying different weight positions. Some development is still needed but I have reached a good compremise. I filled the front nose of the car with blue tack I leveled it on the line where the chassis meets the under pan. I then added a square of lead under the motor after removing the plastic strips. I then place lead each side of the guide position. I have fitted the MJK tires to suit the FG. They are a bit larger than the original tires so it does increase the chance of tipping in corner.
To help overcome this I have placed weight on the door sills . I place more on the LHS . . I also added some weight to the back corner of the chassis . Also on the left side. This covered most of the problems as most of the corners it was having trouble on were left hand corners. The "Folden" is lapping as low as 8.1 seconds.