In general, many of the early Millers Falls planes were knock-offs of Stanley tools, but their sizing & blade angles varied slightly. This may be why your GGF had both types, in order to make/get different results depending on the need (my grandfather had a rather extensive mix of similar hand tools, where an oddball/other-brand tool would be used to "fill the gap" in-between the selection of standard-type tools when needed).
With the rosewood handle & knob with slot-head screws on your MF plane, it appears to me to be either a later Type 2 variant of the 1936-41 production, or an early Type 2 from the post-war 1949-55 second production (I say this due to the fitting of a
steel knurled adjustment knob rather than a brass knob). Like this:
You might be able to better verify which of the two productions it came from by looking at the little inverted triangle on the cutter stamp. If it says "
Since 1868", it's definitely from the first production. If it just says the date "
1868", it could be from either production run. If it says nether one of these, it's from the post-war run (though unlikely to have this due to having that steel knob,
if original).
The model number(s) & the brand name should be stamped into the left face along the
lower edge, below the "camel hump" section of the side brace (see photo above, you can barely see the stamping on it). If you can find it, you can look up the model & relative value here on the OTH site:
http://oldtoolheaven.com/bench/benchtable.htm
http://oldtoolheaven.com/price/price.htm
If you have more MF bench planes that you need to identify, here's a good run-down of the years & variations:
http://oldtoolheaven.com/bench/benchtypes.htm
