Can a 1977 Chevy truck rear end fit on 1968 truck?

It's unlikely a 1977 Chevy truck rear end will fit a 1968 Chevy truck without significant modifications. While both are Chevy trucks, the dimensions, mounting points, spring perches, axle width, and possibly even the differential itself changed significantly between those model years. You'd be looking at potential issues with:

* Spring perches: The location and shape of the spring perches where the leaf springs mount are likely different.

* Axle width: The track width (distance between the wheels) may have changed.

* Differential: The differential housing and gear ratio are unlikely to be compatible without significant work.

* Brake system: The brake system components and mounting points may not align.

* Shocks: The shock absorber mounting locations might differ.

You'd essentially be performing a major rear-end swap, requiring fabrication and potentially custom parts. While *possible* with a lot of work, it's not a straightforward bolt-on job. It's far more practical to locate a rear end from a more compatible year of Chevy truck. Researching rear ends from 1967-1972 Chevy trucks would yield a much higher chance of a reasonably direct fit.