I have a Fleming Sear and I can take the trigger pack out of the 53 and change out the extractor and shoot it in my 91 host or 9mm K or my soon to be MP5/10mm!!! I would go with a Sear Pack rather than a RR unless you have lots of cash for many RR guns, GYZ
And to answer your question: The sear pack will fit on any 90's series weapons with the correct C&P'ed lower, GYZ
Does that mean i can have a burst pack installed on a 53 and the sear would work and then i could take the sear and put it in a 90's series with or without the burst pack and it would work if the weapon is modified to accept the sear?
You guys have been giving me awesome info, thanks so much for the advice !!