What spark plugs are you using? The stock plug for these is the NGK BP7ES .....
These are available at most auto parts stores now for a much better price than getting them from a cycle shop. They can be bought in a 4 pack and I suggest you get that so you have spares while sorting the bike. The 4 pack will run you about $10. You'll also need to gap them. They usually come gapped for cars somewhere in the mid to high 30s. Bike ignitions, especially on old bikes like these, aren't as powerful so the gaps need to be smaller. Set them to .028". I fixed a new guy's 650 once that wouldn't start simply by properly gapping his new plugs. He just stuck them in without checking them and the gaps were too big for the stock ignition to fire. Your hard starting could be related to this.
I think you're giving the P.O. more credit than he's due by calling him "incredibly knowledgeable". Granted, he knows more about motorcycles than you do, but just look at the hack job he's performed on what was a perfectly good motorcycle, lol. The '77 model is one of the most sought after and desirable versions of this bike, a true classic, and that moron took a sawzall to it, lol. And he didn't even do that right, removing things you need (centerstand mounts) while leaving others you don't (original footpeg mounts and lower side cover mount tab).
Here's a short list of things you should investigate .....
- your fork lowers are backwards, mounted on the wrong sides and facing the wrong direction.
- your air filters appear to be the cheap K&N copies which don't work very well at all on these bikes.
- your axle looks to be adjusted all the way back. That means either the chain is all stretched out and shot or "Sawzall Sam" fitted a smaller rear sprocket but didn't shorten the chain for it.
I'm sure there's many other things that need sorting. That's about all I could pick out from the couple included pics.