It won't be just the chassis you will have to buy knowing Tamiya, you will probably find that the chassis halves are in one bag, the motor mount in another and the new arms in a third.
Also it's taken them well over a year to release the M06 style shock mounts for the M05 Gold Edition and they still don't sell the M06R rear hub weights and shock mounts even as a spare part, you have to buy the whole kit to get them.