Scout2 Brake Master Cylinder Differences

[alice@domain.elided]

Hello,
Last night, I bought a rebuilt brake master cylinder from Autozone 
for my 75-76-77-78-79 hybrid D44 front disk Scout2.  The new cylinder 
looks different than the one it is replacing ...the new one has 
crosswise two wire bails holding the lid on ...the old one has one 
long lengthwise bail for the lid.  It appears the new one has larger 
reservoir volume with the same bore (1-1/8"?) and mounting ears.  

Are the internals identical, just the reservoir different?

Is my old one the wrong one? ...wait, but haven't I seen this 
type on a number of mid-to-late 70s Scout2 models? 

What gives?  All help appreciated.  Mark