Will a 21R engine bolt to a 4DR5 gearbox?

The 21R engine and the 4DR5 gearbox are not directly compatible, as they belong to different engine families with distinct designs. The 21R is a petrol engine, while the 4DR5 is a diesel engine, which typically means they have different mounting points and bellhousing designs. Adapters might be available, but significant modifications would likely be needed to make them work together effectively.