Thanks for the comments, everyone! @Maxo: I recommend replacing the SPC you have with the one I posted here, since I made some tweaks to the port since I showed it to you. Everything I do is a WIP lol. And since we're on that topic...
One person ran into problems with Factory Inspection in-game but it was actually just a faulty custom sprite's doing, but in the process I ended up testing the port in-game a bit more and noticed that the global volume was a bit low. Same with Frosty Grotto, so I'm releasing updated versions with higher volume, normalized to SMW's volume using the course clear theme as reference:
Shiver Star Stage Select is meant for maps so I'm leaving its volume alone. Please tell me if it also needs tweaking. I'll be editing the first post with the updates.