dvla engine change notification.

[tas350]

I am changing my Striker 1700cc Crossflow to a Zetec 1800. Do I inform the DLVA that the engine cc has been increased or that it is a completely different engine. I have read on other forums that you have to have receipts for the engine and various certifcate of competence for changing the engine etc. The engine was obtained from a local scrappy 3 years ago and no way will I find any receipts relating to the engine.