I'm wanting to mount a Zenitco B-21m handguard, B-22 optic rail, & an Ultimak M-19 to my KP-9, but I am unsure if there would be any clearance issues between the B-21m & the M-19.  I still want to be able to utilize the iron sights, while having an optic, & remote switches mounted at the 12 o'clock position around the handguard area.  This parts combo would seem to be the ticket for achieving that, as long as they'll actually fit around each other.  Again, the main concern is between the B-21m & M-19.  I think they'll work with each other, since the M-19 obviously fits into the factory handguard & the B-21m appears to very similar external dimensions to the factory handguard, but I'm not sure about the interior ones, & don't want to go buying parts which won't work together.

TL/DR: halp plz?!

shouldn't have any problems with an Ultimak

Not sure how useful the sight rail over the rear sight would be.

Well, after looking at every picture I could find online of railed upper hand guards, any kind of pressure switch would appear to block the front sight post when mounted at 12 o'clock on them.  The Ultimak offering does away with the upper hand guard all together, by integrating the 1913 rails into the gas tube & lowering the plane of the rails.  I know it's not a gas tube anymore, on a KP-9/Saiga 9/Vityaz type of AK, so, I wouldn't be concerned with it getting to hot & damaging anything or burning my hand.

The B-22 bolts directly to the B-21m, so, any optic mounted on it will be rock solidly attached to the gun, & it also raises an optic high enough to not block the rear sight.  Yes, KP-9s come with a dust cover with a rail system attached to it, & the dust cover reliably let's optics mounted to it return-to-zero after the cover is opened & closed, but any optic mounted on it will block the rear sight.