Side repeaters won't be an issue, but I suspect emissions maybe. If the car was SVA'd and is just 3 years old, then it must have had a cat fitted, therefore getting through without one will be difficult. I would get it tested first if you can, as I believe, (could be wrong on this) emissions don't fall under the re-test category, therefore it will cost you for another full test when you go back.
Also, my MOT station informed me that, now the MOT is computerised, once you fail, the car is off the road, as its listed with DVLA as a failure. So you will only be able to drive the car back to the MOT station for a re-test if needed ☹️ This they told me is even the situation if you still have a current MOT running, so getting it MOT'd early seems a bit of a risk now.