petey, I have not used either as I am fortunate to have my original 99M1 rear sight.

However FWIW:
The first link seems to be for a Picatinny rail. While you can mount a P-Rail on your 99M1, it does raise the height from the receiver and may not work.

The second link seems to be more for a .22 mount and may be more appropriate for your 99M1. It may work, and work well, but if you're interested in getting your 99M1 close to original, it won't do, as it is totally different.

In terms of functionality, the second link seems to be preferable. I toyed with a small scope on my 99M1 for a bit but switched back to the original rear sight (likely mostly because it was a crappy old scope). Primary reason for going with a scope was a front sight that was loose, with a stripped screw. I have since fixed that, courtesy of Numrich...

The 99M1's accuracy is great and would benefit from a small scope, but I prefer the handy aspect of the original design for a handy light-weight carbine - not a sniper rifle.

Just my opinion, which combined with 2¢, doesn't even get you a coffee at Dunkin' DoughNuts...

 

I had a Williams peep similar to the one you posted on a model 60 that worked great. Don't have it anymore so not sure what the exact model was. Might have been the same one.

 

I put the WRGS-54 on a Glenfield 25 and needed a taller front sight, it may work with the existing 99M1 front.

Alternatively, if you can do it or don't mind paying a gunsmith to drill a hole, I put Tech Sights on a 99M1. The rear is straight forward and I drilled and tapped the barrel to mount the front.

 

The UTG is the lower profile of the two and may work with the stock front sight. Put one on a High Point rifle a few years back, as it was the lowest I cold find, and had to cut and re tap the front sight insert to get it low enough. Worked ok for the gun owner but to me the aperture was too big for close work.
Luckily I never removed my M2 rear sight when scoping it many years ago.

 

Thank you one and all for your input. I think I will continue my search for an original M1 rear sight to make it original. In the mean time I have a vintage Marlin 4x micro-vue scope that I will put on it. Looking at images with and 99M1 and 989 M2 with scopes, it does not look that bad with the smaller scopes and it may even dial in a tighter groupings.

 

Sounds like a good plan. I used a crappy 4X Tasco 22mm scope for years. Wasn't great but hit things I aimed at reliably when I could line things up. For a while. Finally went with a 10/22 and then with a 3-9X32 Simmons AO scope on the 10/22 (great combo!). Kept my 99M1 rear sight and put it back on, replaced the faulty front sight and went back to irons on my 99M1 rather than a scope. Happy with both!

Be patient!