Thanks, Woody. Yeah, I looked around Thingiverse and saw a bunch of cases but was hoping TH3D made their model available so I could figure out the one with the least mods. Now that I read up on heat issues with the Pi4 I was thinking I'll need better ventilation so I might use an existing Pi4 case model, abandon the rail mounts, and screw the whole thing to the outside of the enclosure anyway.
I was expecting a more noticeable performance improvement than you report though, based on Sanladerer's quick-n-dirty benchmarking of Octoprint, but it's as much a learning exercise as anything. I just want to build one up from scratch and a spare Pi4 is what's on hand at the moment. The case won't even be needed if I can't get it running so perhaps I'm being prematurely optimistic. Time will tell.
Thanks for the reply and advice!