If the serial number starts with MOW, then it definitely isn't a Spaceliner (or any other bike from Sears). Sears serial numbers begin with 502.
MO signifies it was built by Murray. Murray built bikes under their own brand name as well as under contract for many other brands (even though Murray built many bikes under the Sears or J.C. Higgins label for Sears, the serial numbers will always start with 502).
The W indicates it was built in 1963 (which incidentally pre-dates the first year of Spaceliner production, anyway).
64 indicates the model (but I'm not familiar enough to tell you what it is).
The X10 indicates the bike was built for Western Auto, which means the bike brand is a Western Flyer. This is the key bit of info. you're looking for.
Once you post a picture, somebody will be able to identify your bike model pretty quickly.