Engine swap legalities

I have an old toyota Yaris and im planning on swapping a Honda K20 into it. As far as I’m aware to get it legally registered it’s easy as long as we don’t modify the chassis. And all i need to do is change the v5c and sort insurance. Am i right in thinking this is all thats needed legally or am i missing some important facts. The car will obviously need a new gearbox, driveshafts and mounts, this classifies as not severe changes as far as the DVLA is concerned right?