I don't have a 618 to measure, and this dimension doesn't seem to be given in any of the Atlas literature. What is the width of one of your ways? And what is the width and length of the machined flat top of the compound slide (ignoring the slot down the middle)?
Yup that's a problem. Full size indicators and stands are tough without taking up all the working real estate.
I have three go-to setups that stay assembled: the full size Noga base and 2" indicator on the front dashboard, a modified (shortened) cheapo base and indicator as a standalone travel indicator at the headstock, and then the small, half-sized base and indicator that can mount almost anywhere but is most useful for the compound. I also have two regular indicators with custom holders that clamp to the ways as travel indicators that aren't shown below.
This is the half-sized one. I'm pretty sure I bought it through Little Machine Shop. The mag part is about 1" X 1" X 1-1/2" or so, with one of the shorty arms I scavenged from a flashlight holder. The indicator is small too at 1-1/4" dial which really helps. Only 0.250" travel on it though, that's the only drawback.
I use a 0.0005 DTI in my tool post for centering work in the 4 jaw and a big azz 50mm dial indicator in a cheap'n'nasty mag base for indicating offsets or behind a feature I can't get to with my DTI. The mag base clamps just fine to the ways although it would hold onto the cross slide dovetail cover too if necessary. One of those small Noga knockoffs from eBay would probably work just fine on a 618, never got round to getting one though.