Yes, they will swap in, but you'd also want to install the little top-out spring they came with or they'll "clunk" every time the forks fully extend .....
Your '77 forks didn't have these little springs but you can add them. The '77 damper rods are actually quite nice. Yamaha put a little more time and effort into manufacturing them. They beveled the oil holes and polished the rod some. Notice how it shines more than the '78 and newer rod .....
You could do the Minton mods to your '77 damper rods. That will improve fork action some, not as much as the emulator but they will help.
I put together what I call a "hybrid" set of forks a few years back, using what I considered all the best stock parts. I used '77 forks and damper rods (Minton modded) then added the '78 and later top-out springs, fork springs, and adjustable top caps. As with most all of the stock springs I've tried, I found them to still be a bit soft. I recently "tuned" in the stock forks on my '83 by adding additional short preload spacers to the stock springs. It took a little experimenting with spacer length to get them just right. I think doing the same to these '77 "hybrid" forks will fix them up too.
