The Outbound Laptop Model 125 only uses four types of hard drive as far as I know, 20, 40, 60 and 80 MB 2.5" IDE drives. I know that the Conner CP20xx variety work in the Outbound. Although now that I'm about to write it, I suddenly have doubts about the CP2084. I think I only ever owned a CP2064 before but always yearned for the larger (80 MB) 2084.
IIRC, Outbound Model 125 compatible hard drives for about $25 by the time one pays shipping.
We really need some 68K machine code hacker to hack in compatibility with larger drives.