Is picking up Deadlands worth it for a western setting?

Recovering D&D DM here (by which I mean I am attempting to drag my players kicking and screaming into this system, I am unsure if it'll be a success).

General order of things (TLDR is in bold in the last paragraph): I pitched 3 possible campaigns to my players towards the end of our last one. They voted for the western themed one (I'd been playing a lot of rdr2 when I wrote the guide). I then gently pitched switching systems because I've had the SWADE rulebook for 3 years collecting dust on the shelf and if I run one more D&D game I'm gonna cry (inside). I've slowly worked them around to "giving it a try" so I cracked open the book (ended up buying the PDF last night because I left my copy at my MIL's), and have started brushing up on my knowledge and re-watching some videos. Poking around on the site, I found the Deadlands setting and by golly it's super similar (but not quiteee the same) as what I've already designed/planned 6 months ago.

But since I just bought the PDF for the core rules, is it super necessary to pick up the Deadlands core rules since it seems that they're similar, or am I probably ok to just run 'er as is? I am a highly improv based GM, I rarely run modules so I'm not looking for help with the game itself, more just curious if having the Deadlands rulebook has any major advantages over the normal rulebook. Would I be smart to just grab a supplement or two (like the Rascals, Varmints & Relics or the Weird West Companion or Hell on the High Plains) for some idea generation/stat blocks or is that going to trip me up without the core book?

If this needs to make more sense, lmk, I've had a long day.