Auto speedo gears and cables

To be honest I never saw any differences in 68 and 78 speedo housings and gears. Not sure why yours is different??? Since they are different you'll have to come up with a speedo gear adapter housing from a trans. like your original trans. had, whatever style that was. Can you post a picture of what the 78 transmission speedo gear housing and your cars speedo cable looks like? That'd be a huge help in figuring out what you have