From the 2 pics you posted, that looks like a gem of a top and excellent doors! I would want to see pics of the underside of each door, and the sill under the hardtop to check the integrity. Those are the first rust problem areas.
When you consider that the fiberglass top and rain gutters look to be in great condition, that's a huge plus! If the doors come complete with glass and all hardware, that's also a major plus. Many doors for sale only include the shells.
As to the year compatibility, the front door windows have the front wings, which I don't think a 77 has. My 76 doesn't have them, but I wish they did! The inside panels of the doors will tell more about the year. Also check that they are steel vs. fiberglass.
With white doors and a dune beige top, they are most likely from different trucks.
Get more pics and look closely. But IMO, all that this setup includes will save big bucks from glass to seals to hardware that you would have to source elsewhere. If you don't have to replace the rain gutter, that also saves some major cost and headache.
Bonus points if the top has a good headliner!
If it checks out, I would go for it and consider myself lucky!