97 and 98 are the same PCM. 1999 began using a different PCM and wiring pinout.

You need to force flash the whole OS segments and calibration.
I would keep the 98 VIN # because if the car ever went to a dealer and a Tech-II is used and if you used the 97 vin then the tech-II or SPS would flash 97 code back into it

For my 99 LS1 I used a 2003 LS6 flash and use a 2003 VIN ID.
This also helps when using a smart OBD scanner like Ease to use the correct PIDs for a 2003 being it goes by what the VIN ID is

If PCM is out of sync with BCM the security light on dash will not flash like it should and could set like a 1636 DTC