You can import anything pretty much. I imported a 78. I went with the 1-GR petrol for several reasons: I know and like the engine, the fuel economy isn't much different to the 1VD or even the HZ. The VD is too complicated for world travel, too fussy one fuel and the 1HZ slow. I would be happy to have a 1HZ but I was buying new and as such it would have to had passed current emission regs and I didn't think there was a chance in hell of that. If you're buying a car over 10yrs old it is much easier as it only needs to pass a MoT not an IVA inspection. If you are importing a new vehicle then left hand drive is much easier to get past VOSA. (seems to just be a 'tick the box it's foreign' almost!)
I think, but may be wrong, that most imports are ULEZ exempt simply because the data on emissions does not exist for them.