90 DX Hatchback VX trans?
 

So, I've owned my ol' Civic for about 10 years now and its been a pretty good little ride but now, with 191k, its in need of a clutch. I've recorded 48-50 mpg at 60mph and know I can do better with the taller gearing so I'm considering swappin' in a VX(or CX?) trans. Will it bolt right up?

Nope. VX is '92-95, as is the US model CX, those years use a hydraulic clutch setup, your car has a cable. Your best option is a '88-91 CRX HF transmission. You can use a later, hydraulic clutch transmission, but there are quite a few mods you need to do to make it work, where as the CRX trans will just bolt in.