Can you stamp aluminium
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I would not worry either, you have learnt a lesson though to always check frame and engine no, first thing I do, historic now anyway. Just enjoy it as is and if the opportunity arises at a later date change cases/engine to suit. Probably hundreds like yours around, dt's are a scumbag magnet that appeal to people trying to make a quick buck. As Calum says any attempt to replicate vin no on engine is doomed to failure and makes you complicit in concealing identity and will stand out a mile.
If it's a good sound engine don't fret, you didn't steal it or know provenance at time of purchase, put it down to experience.