Ended up transferring node data "by hand" - needed to see type of polling (WMI, SNMP, etc.), what credentials were being used, and if they worked. Didn't seem to be possible in any sort of an automated way.
There were also default alerts specific to NPM (mostly to do with interfaces) that were not there on SAM: as HolyGuacamole mentioned, exporting them and then importing did the trick although some got broken in the process (lost their trigger conditions).
The installation itself was uneventful and didn't require any intervention.
Didn't transfer the license yet - leaving that until I am 100% sure the new box is fully functional.
Thanks for the help and for the tips!