The RPK retainer is way bigger than that of the NHM...looks like I cant take enough material off the lower to fit the CHi-Com retainer...Any suggestions as I see plenty of RPK stocksets on the NHMs???

The RPK retainer will not fit the -91 barrel either. The RPK barrel is much larger in diameter. I just faced this problem last week.  If the swap is something you must do I recomend glueing in a plug in the front of the RPK handguard.  It's a lot of hand carving, but that is one way to go.  You might try epoxy mixed with a filler but the handguard won't fit without some improvisation.  Fiberglass matt would be an intresting way to go as well, if you know how to do it.  There is no reason this can't be done.

I think i stated this a little confusing..I am trying to fot the RPK lower handgaurd to the Chinese retainer plate...

If i remove material from the HG there will not be a whole lot left ont the tabs front of the Hg that goes into the retainer...

You are correct. You'll have to cut off the RPK hand guard material that fits into the RPK front hand guard retainer and cut away more material out of inside of the RPK handguard so you can glue in a block that is small enough to fit in the -91 retainer. You cannot fit it otherwise.  There is not enough wood in the RPK handguard, for it to be secure. It can be made to fit, it will not "drop in".