motor mounts were almost a bolt in, I used the datsun throttle linkage, the datsun trans mount had to be widened and bolted to the floor; the original bolt holes couldn't handle any offset without tearing.
the hardest thing was the clutch linkage; the Hillman used a cable, datsun has a hydraulic linkage, i used a '80 honda prelude master cylinder bolted to a bracket welded to the pedal box with a remote reservior. I also had to have a custom driveshaft made and move the shifter hole back slightly

That would be easier for us then cos our 60 series use cable clutch

These were known as an avenger in NZ/Aust/UK.
The original running gear was sh1t. A nissan transplantn would make it into a good car.