I have a '95 DX hatchback and recently swapped in a CX (same as VX) tranny. It took me and my friend (former Honda mechanic) w/ his air tools just over 4 hrs to do it in his garage w/ the front end jacked up on regular floor jacks. Some of the time was spent recording the RPMs w/ the old tranny and new tranny (to know the difference after the swap), and about 20 minutes to re-tap a couple of threads on the new tranny. All said, it was an easy job, but two people is highly recommended.
Regarding FE improvement....I haven't had enough tankfuls nor the same exact driving as pre-swap (i.e. I'm driving slightly faster now due to longer trips...can't afford the extra time driving 50 - 55 vs. 60 - 65) to determine the FE improvement. Also, I recently bought new LRR tires that are skewing the mileage. My best guess based on conversations w/ another member who did the same swap last year (look up scostanz) is that it improves FE by about 6% -10%. For me lately, w/ a lot of engine off and engine on coasting, the improvement won't be as substantial because much of my FE gains come from this coasting. For others who do a lot of straight highway driving at 65 mph, the FE gains will be greater because the RPMs are being lowered by 500 - 600.
You can find a good used CX or VX tranny at a boneyard for $50 - $200. Check out
www.car-part.com. I bought mine here for $150 shipped..it had 60,000 miles on it.
Steve