Here's some good info for you:
All g-series are created equal. Here is a quick list of cars the G-series comes in (and that this diff will work with):
87 Mazda 323 GT
90-94 Protege LX
91-94 Mercury Capri XR2
91-96 Escort GT, LX-E & Mercury Tracer
92-94 MX-3 GS (pos 1.8 v6)
93-97 MX-6 (both 4 and 6 cyl)
93-97 626 (both 4 & 6 cyl)
93-97 Probe (both 4 & 6 cyl)
95-98 Protege ES (1.8 dohc)
97-99 Kia Sephia (1.8 dohc)
97-present Ford Escort & ZX2's (i'm not sure of this but ppl tell me they use G-series too)
98-01 626 4 cyl (not sure about 6, i forgot if its a k-series)
01-03 Protege w/FS motor (2.0LX, ES, MP3, Protege5, MSP, and in 02' all DX and LX's got the 2.0 standard)
04-??? Mazda 3
Basically any car with a 1.8 BP, 2.0 FS, or any K-series V6 has a G-series transmission, even the Miata. Theoretically you could swap the 6-speed Miata tranny guts into a FWD transmission (if it'll fit in the bellhousing).
Kinda interested in testing this out and grabbing a tranny from one of these from the junk yard and repacing my 3rd gear....