new Umarex version looks the part, but really isn't a patch on the 'genuine' thing.
I've given a couple of Maks a new barrel which has a thread on the end, then you can add a silencer. Which is nice.

Don't know about adding optics though.

check this man, who has done loads to his Mak, including machining off some of the breech. He inspired me to chop 1.5 inches off the springs, as it is RIDICULOUSLY heavy to cock.
And how to open bottles of beer.

Note the pronounciation, which is: muh-KAR-ev, which was how I pronounced it t'other day to a Russian customer, much to his delight. He did point out that they are crap