I mean... given it's already assembly it should be easier than normal to reverse-engineer it, no? Or do you think there's lots of nasty low-level hacks in there that will be harder to decipher?

I've tried disassembling the version of RCT 1 that's on Steam, and the program starts by, IIRC, decrypting the other parts of the executable before jumping into it.

Steam uses DRM, does it not? So it could be that, and in that case, perhaps the GOG version gives better results, since they claim to be DRM free.

https://www.gog.com/game/rollercoaster_tycoon_deluxe

As far as I know, the version on Steam is the same as what came on the discs with the only modifications being some patches for compatibility. There were also no references to Steam's DRM anywhere

The assembly code might well have been created with lots of macros.