Only mods I made too my MAk-90 was a Williams peep to my OEM ladder rear sights. It is pre-thumbhole folding stock and a machined receiver vs a stamped. Very strong and durable. All I brought home from the wars were “real” AK magazines and some better spare furniture. Great little working gun that is really reliable and a nice rig for folks to cache due the design of the springs !
http://www.ak-47.us/MAK-90.php
Just my opinion ........!!!
My SLR100 is all gussied up with a quad rail in the front, bipod and side attaching scope rail. The list of wants for it are a folding stock and new trigger group and a recoil buffer. But since I just got the AR it is likely to be gathering dust for the next few months.