You can use a type 3 GB, though it will have 2 pin holes in stead of 1. And a Bulgarian FSB, though they're 'open' instead of hooded. If you find a hooded Chinese FSB it will be $200-$250. A GB probably around $100.
I have done exactly as suggested above, but it isn't "correct"since the stamped MAK90 uses stamped type barrel components, and a wire-cutter type bayonet.
The problem with the Chinese guns is that they are hybrids, in that the stamped MAK90 has a milled diameter barrel, so every other country stamped AKM parts won't fit. Only milled type parts will fit, such as Polish or Bulgarian. But those are "wrong" in that the fsb is not hooded, not the same as the stamped fsb, the gb has no bayonet lug, two pin holes, etc.
The real problem is that original/genuine ChiCom parts are extremely unavailable. A hooded fsb with the correct design (many/most MAK90 fsb & gb were ground off/neutered) are not found or if they are, are super expensive.
The correct bayonet for the stamped MAK90 will be the wire-cutter AKM style, not the type 3 AK knife style. So people compromise by replacing the fsb & gb with milled components, which fit perfectly, then mount the older style bayonet. Not "correct", but only someone who knows what they're looking at can tell.
I am thinking about going the 'conversion route'. I'm not so concerned with 'correct' but like the look of a 'standard' AKM with cleaning rod and similar blocks. Got a Bakelite furniture set on the way, which is not really 'correct' - just cool. It can likely cost $250 to repopulate the two blocks anyway - especially if you need to cut another pin hole in the GB (Type 3). I suppose the milled barrel FSB and GBs are available?
Thanks - good information here. (thought I had remembered the deal on milled-type barrels).
I would be sure to measure them against the barrel first, to make sure, but yeah, should fit. Milled Bulgarian are what I used. The Chinese gas block only has one retaining pin, so that's a difference, the Polish & Bulgy type3 parts will have 2 pin holes. You'll also have to drill the lower handguard retainer for the cleaning rod hole, so do that when the gb & fsb are off. Dont forget to out it back on!