SGD-R35-71x80 latch part

Thanks for posting. It looks like you're missing your mortise lock. Based on the shape, I think our 82-218 is what you want, but review our dimensions to confirm that it will fit in the space available. Take a look and let me know what you think. The video below shows how to install this mortise lock. 

Thanks for getting back to us! Glad you were able to get a mortise lock to work on your door.

As for the spindles on the lock set, it depends. In my experience you rarely have to trim down the inside thumb latch, but in your case it may in fact be necessary depending on how thick your door is. There's no surefire way to know exactly how to cut these spindles right the first time. Your only option is to try them out first, try to determine which side needs cutting (or both sides, as the case may be), then cut off one notch and try again. If it's still not enough, take off another notch and try a second time, and so on.

I know that's a time-consuming process, but it's better than cutting off too much. Then you're kinda screwed, since you'd need an all new handle set. Just take it one notch at a time and eventually you'll find the right clearance. This is what I do and it's never failed me. 

The video below may be helpful. It doesn't feature the same exact handle set that you purchased, but it demonstrates how to properly cut down the same kind of spindle.