My Alecto is *super* quiet with a moderator, I actually thought the gun was broken the first time I used it. Same thing when I made a mod adaptor for my Beeman P17. I presume it is because pneumatics are very efficient with air and the knock open valve itself is quiet in operation..

A 1377 will not be that straightforward to get a moddy onto, unless you get a longer barrel, and then it will be a piece of cake - Crosman adaptors are everywhere.

The thinner profile moderators that you can get - and I suspect this is the same thing you are talking about for the Makarov - are not nearly as effective as a full size moderator, although they do take the sting out of it. Their big plus is still allowing you to use low profile iron sights. I picked one up from Versandhaus Schneieder and it now languishes in my airgun bits box.
If the weight of a full size HW moderator is too much on the end of a pistol, I would suggest the Pax carbon fibre moderator, which is very light and only a tiny bit less efficient than a HW mod. That's what I have on the Alecto.