I just received my Polish Beryl Picatinny Rail Assembly from RTG. I now realize that this is useless unless you have Beryl rear trunnion installed. I also received a Beryl Lower Handguard Variant B which I found that once installed the cleaning rod will not clear the nut & bolt that holds the vertical grip on. I have no idea where to get a Beryl rear trunnion and even if I had one it's not going to be an easy install. The cleaning rod issue I  may be able fix by grinding down the nut, bolt or both so the rod clears. Does anyone have a soulution to these issues?

I've been eyeballing those rails, too, but I knew the rear sight block wouldn't work as is.

I was thinking about trying to find measurements for the beryl rail cuts, and have my rear sight block modded.  It appears to me to be two slots cut into the sight block... no rocket science (as long as they are the right size and in the right place).

FWIW, I've never seen the beryl rear sight block advertised for sale.