On e-bay a CCKW vendor is selling a Zenith 28AV10 and claims that it will 'work' on a GMC270 in a CCKW.
Ok, from Zenith Technical Bulletin Z-190-B (Aug, 1950) here is the codes for what the last two digits on the model mean:
Note that the both the Nominal size and Throttle Bore are both 1/8 inch to small when compared to a 28AV11. While the Flange size is the same, it will 'bolt up' but you are gonna have some issues with power as you have a small bore to get air through.
Also, the 28AV10 is like the 28AV11 in that the air cleaner is held on by a clamp around a flange at the top of the air intake. On a CCKW that flange is 3/4th to an inch high. The 28AV10 has a much smaller flange.. *maybe* 1/2 inch.