Where is the engine number on a PRV V6?

[CitroRS]

Thanks @dieselman for the link.

In general I wouldn't be bothered too much, but there is one unusual problem here.

This XM I'm talking about was imported in 1995 from Switzerland, and had V6 engine removed in 2006 when 2.0 was mounted. I was lucky to track down and buy it's original V6 engine, one with the number 1FV54***. Since car was registered as 2.0 model since 2006, I have to go trough homologation process again after fitting V6. Out of many papers I need, one is confirmation from official Citroen importer that this car had SFZ engine with 1FV54*** number initially mounted. Problem is that service.citroen shows engine number is 10FV5400*** instead 1FV540***. Last 6 digits and SFZ engine type match. There is a problem with service.citroen database, it even lists this XM as XM2 with V6 24V engine. On the other hand, when I check chassis number over partslink24 it shows data as it is, XM with V6 12V engine. Probably when service.citroen was established, old car data was bulk-imported, so that's why there are so many mistakes.

This wouldn't be a problem generally, but in Serbia engine number still plays important role so all documents I need for homologation must have exact engine number in them. Yesterday evening I googled a bit, and found SFZ engine that has number stamped in same form, so my guess is that maybe difference was in production date, production lines where engines were built, machine setup... I think I will be able to sort it out, even got complete history from police vehicle department, from 1995 onward.

[Dieselman]

What letters are in the Vin?
The letters denote the engine type, V6-12v and V6-24v are different, also Series 1 and Series 2 and saloon/estate variants.

I'm sure you are aware that Y3 is Series 1 and Y4 is Series 2.

The simple answer is to ignore any numbers before the FV part of the engine number, as I don't think Citroen record those, alternatively use whatever is available from Service.Box, as that is what is held on record.
I believe the engine numbers were hand engraved, or the characters manually selected, and it appears one of the zeros is in the wrong position.

I understand the issue you have, the registration authorities need to establish the car is the actual, complete car, otherwise it will be issued with a "kit car" registration.

If all else fails speak to the Citroen importer for Serbia, as they should be able to obtain the original Homoglogation certificate.
Good luck.