You have to use the diesel transmission front case with the diesel engine, the starter is on the left side on the diesel engine, and the gas engine has the starter on the right side.
Are you putting the diesel engine in the gas engine frame, I ask because the diesel engine mounts differently than the gas engine, the easiest way is to cut the diesel frame mounts off the diesel frame and mount them on the gas frame after you cut the gas mounts off, you slip the diesel engine/transmission into position and mount the transmission on its mount, connect all the mount hardware from the diesel frame to the motor mounts, then drop the engine onto the frame making sure the diesel mounts rest properly onto the frame, then tack them into position, then remove everything and weld them to the frame.
Is this the Clive I know in Australia, I am wayno.
I have a few Datsun/Nissan diesels, my 521 kingcab is a SD25 diesel.
I forgot to mention that you will need a diesel engine 4X4 oil pan, they are different than the gas engine pan, so you will need to find one unless it already has one.