The very first variation in Gunpla history is the 1/144 Mass Production Zaku — essentially the 1/144 Char's Zaku with a different molded color. Visually, the only difference seems to be the head antenna, but in the case of the MG, the leg and backpack verniers are also different to reflect the "three times faster" setting. That said, old kits are old kits — the verniers weren't even molded in the first place, so aside from the head antenna, it came out as a structurally 100% identical kit.
For more detailed photos, please check out the 1/144 Char's Zaku review— and the Mass Production Zaku still shows off that wonderfully nostalgic, old-school proportions that bring back all the memories. From a molded color standpoint, it looks a bit more grounded than the Char's unit with its food-toy-esque dodgy sausage color — this one's got a brighter olive drab that feels a little more put-together.
Either way, as one of the historic Gunpla kits, this is the kind of thing you really should build alongside the Gundam to get the full experience. :-) [ Updated at 2016.1.7 ]
AIThis page was translated by Claude Sonnet.