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It is possible that it is a number assigned by a state authority when the original was not found on the chassis. I have had this done to several cars I have owned in the past (years ago). For example, my 1960 Citroen when I moved to Victoria in 1971, there was no number to be found stamped on the vehicle - the number stamped on the attached identification plate was not considered valid, as the plate could be moved. It acquired the number V161P from memory - the V and P designating that it was put on by Victoria Police.
However, these numbers should have a state designator letter and end in 'P'. (But similar schemes may have existed before this that did not match this pattern)
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I'd be tempted to get the chassis number sorted out before you paint. No point finishing the resto and finding you can't register it.
Where is the number in your picture stamped ?
As mentioned by others the chassis number appears in different locations depending on the year, where assembled etc.
Mine, which was assembled in Australia, is on the top of the passenger side dumb iron close to where the bumper mounts.
The number stamped doesn't match the Land Rover numbering system.
Land Rover FAQ - Repair & Maintenance - Series - Chassis Numbers, by Type
The 'brake loose' stamped on the chassis is very odd. Painted on might be a roadworthy comment but stamped ?
Colin