Welcome to the wonderful world of "someone machined off the choke horn to eliminate the "restriction" (it does not cause) and did not transfer the list number to the carb body again". I would suggest as you get this nailed down, you do yourself and the future owner the favor of stamping the list # back on.
From a dig on the web, you're not the only person to have this exact problem:
The next guy at least had the choke horn still on:
The 4160 has a non-jetted (fixed jetting) metering plate in the seccondaries, and a vaccuume seccondary.
The 4150 has replacible jets and mechanical seccondaries.
At last resort to spec out the CFM, a set of calipers and a call to holley should be able to get the CFM of the main body.
All the list 1850's I am finding specs on, are 600CFM'ers. Apparently no other size.
No restriction eh? why dont they put them chokes on the hp holleys then?