[Jack_Bauer]

Can a burst trigger pack from a 91 go in the 21E trigger housing?

 

[G3Kurz]

Can a burst trigger pack from a 91 go in the 21E trigger housing?

Factory parts - no.

 

[MOAxp]

While it may drop in - it will not function correctly in the E - different ejector clearance cuts, different sear/safety catch and different hammer relief from what I recall - but I defer to G3Kurz final word