Although I am not building a Z-cars mini I am building a front mounted R1 mini and the principle is the same. Space is a bit of premium in the mini so the engines are mounted sideways as they would be in a bike and linked to the wheels via chain-drive differential. I purchased my chain drive kit from Westgarage. It uses a mini differential, output shafts and output covers with a custom machined oil can and sprocket. You need to fabricate a mount that allows you to tension the chain whilst maintaining the correct position for the drive shafts. (have a look at my project in my signature)
I'm sure there will be loads of pictures in the build sections.
Some kit cars mount the engine front-to-back and use a gearbox adapter so that the engine drives a shaft connected to a rear wheel drive differential. Check out locostbuilders for more details of that approach.