Sometimes even the van vin# will not help, as was my case. The van mine came from was a gasser from the factory then re-powered some time later. The division or company who did the re-power is now defunct and I can't find any info. I called Cummins Tech support and they told me none of the B series engines have a block s/n stamped anywhere. I have heard some people say the s/n might be stamped on the back side of the head but Cummins disputes this. Besides it makes no sense to stamp a block s/n onto a head, the same would hold true for the engine ID tag being mounted onto the gear case. I asked Cummins about this too and they didn't know what to say.
Of course it's very important to establish a very sound paper trail when building a project vehicle. It won't help much in recovering your losses if you accidently bought stolen parts, but it will keep you out of the hoosegow [how the heck do you spell that?].
I have never had a law enforcement officer inspect my engine number, but not to say it couldn't happen. Also I didn't go down to DMV and tell them I installed a Cummins in my truck either, and never had them ask. I would guess that the main problems might show up on a later model vehicle still under smog regulations, with no potential problems on an older vehicle that's smog exempt? Still, the CPL number is handy for parts sourcing.