Why would anyone put such a huge low rpm engine on a slayer?
I've never put a big block on a revo but there are quite a few threads in here if you search for them.
You're better off putting a smaller, relatively speaking, higher-revving engine in it like a .21 or .26. I personally like the Picco .26 Maxx.
If you just have to have that motor, you'll need the Traxxas Revo big block kit. I'd also suggest upgrading to a New Era motor mount and a better pipe like a good THS.
Pretty sure the only way you will get it to fit is either with the starter housing replaced with a solid backplate or thinner roto-start and the traxxas big block kit OR the new era universal big block mount.
New Era doesn't make them anymore, but a forum member here is making some similar. He borrowed my NewEra mount to make the template. He's still working on it I believe.
That's not too much different than what NE was selling them for when I bought mine forever ago, I think I spent $75'ish. They slowly jacked up the price to $90 but now they are like trying to find unicorns... $60 shipped is a damn good price for that.