If I get a different engine for a rx7 how to register it ?8
 

If u have any idea I would be happy because it's really urgent I've got a rx7 thinking to get another cars engine but it's not a rx7 engine it's a 1jz engine how to u register it soo I won't course any problems at all uk

A quick search yields this:

https://www.gov.uk/change-vehicle-de...idence-to-give

I don't know if you have any e-testing in your locale, but likely it will still need to pass the emissions based on the vehicle that the engine was donated from. ie. It would have to pass emissions for the Toyota it came from.

Additionally, if you have a safety/certification inspection in your area, it may be illegal to remove emissions equipment. So if it came from a car with cats and an air pump (as well as EGR valves and whatnot) you might need to make sure all for those are there. I don't know if this is the case for you, but I know it is the case here in Ontario Canada.

Not to be rude, but the cadence of your post suggests that perhaps you haven't investigated this enough. I suggest before you spend any money on an engine or begin any work, you not only investigate the legal and emissions requirements of the swap, but how much work it will take to complete. A swap of engines is not trivial, you will need to fab all of the engine mounts and transmission mounts, adapt the trans output to the driveshaft (if you retain the Rx7 rear end that is), adapt or replace your cluster, install a standalone EMS (or the Toyota ECU, if you can get away with it). The considerations are numerous. It will be a lot of time and money you will have to invest to get this done right. If you don't do it satisfactorily, they might be able to deny you registration.

I'm not trying to discourage you, just don't want to see someone start a swap without knowing what they are into. Good luck, and let us know how it goes (maybe a build thread?).