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I have a 77. And I know 78 and up are different to 77 and down. but I am certain they still come apart in sections. several of the parts vendors have how to videos. suggest you check out Wilcox and Zip for there tech videos .
It is only one piece, Willcox has a great description of how to do it, but it's a big job and I found it impossible to get it out without breaking of one of the end tabs (you have to bend these up and after 40 years mine was rather brittle). Also I had the windshield removed, it's probably a bit more difficult with the windshield in place.
I've rebuilt or replaced most everything on my '69.
By a wide margin, reinstalling my main dash (spedo and tach section) was the most aggravating job I have done.
I would research your car very well before deciding if it's really worth it.
I've done my 79 when i had to replace the heater core. I found a great write up here, but it was at least 5 years ago and i can't find it again. Bascially, you have to remove both gauge clusters, the glove box, the wiper and light switch, the cover under the steering column, I believe the dash speakers have to come out, the kick panels, the A pillar trim, and I think i remember that it slides in place on tabs around the windshield. I did mine with the glass in. You'd be smart to let it sit in the sun before actually removing, or installing, so it's a pliable as possible. I think I covered everything, but could have left some items off. I wasn't hard, just took time.