Replacing sight-glass and couplings - what am I in for, what do I look out for?

My sight glass is leaking, and I have an appt. Tuesday for a service person to come help troubleshoot a fix. In the meantime, I need to also learn more myself. (This is also the same service person who may be evaluating replacing the auto-feeder from my other thread, but this seems to be a separate issue occurring in parallel.)

As a separate issue to repairing the glass and leak, whoever installed the fittings for the sight glass reversed the top and bottom position of these L-shaped fittings with the valve perpendicular to the fitting elbow, and instead of swapping top and bottom so the valve exited on the observer's left, they removed the valve handles because they would have impacted against the other Y-fitting that goes to the auto feeder.

Why they didn't realize this is something I can't say, maybe there's something I don't know, but swapping top and bottom would have given plenty of room for the handles. There is plenty of room where a handle could be parallel to the elbow (as I've seen in other fittings) or exit on the observer's left.

However, the bottom stem that the handle normally screws into has been opened/closed so many times with pliers, I am very afraid that it will not be able to be opened/closed much more, and while I have it leaking quite a bit, I have opted to close it so my boiler feeder isn't kicking on each day to fill things again. You can see in the pictures that the top stem is relatively unmarred, but the bottom one is badly mangled and almost half of it is worn away from the plier's teeth.

So I have 2 things to fix: the sight glass leak, and then the fittings themselves. I used some calipers to measure the outer diameter of the fitting's threads the best I could and they measure .85 inches, or 17/20ths, which seems dang close to 3/4 given there is gunk on them and the threads may be slightly wider when measured than the fitting's labeled size.

I am looking at this replacement kit on Amazon that says it is 5/8", so I am not sure if that would go right into the Y-fitting that you can see in the picture.

If it would fit, what is the procedure for changing the fittings and replacing the whole sight glass assembly? I presume I'd depower the boiler and open the valves and drain the water down below the level of the lower valve, and then just unscrew the compression nuts and remove the glass, then unscrew each fitting from the Y's and put the new ones in with some high-heat teflon tape, then cut the glass to size and apply the compression nuts, and we're good as new?

And a somewhat obvious question I still need to ask: could I swap the top/bottom fittings and keep them if I can't find replacements right away? This would put the valve with the mangled stem on the top, and the one that is still intact on the bottom where I could reattach a handle properly. I know this is not ideal, but between finding the right parts, getting the right knowledge, and the right service help, I still have a few weeks of heating before I could consider going without hot water.

Okay, thanks forum folk, guide me as you have done so well in the past!