Sorry about posting the wrong info. Your sear supposedly will work in a select fire lower. Asked a friend of mine over coffee this morning and he is a total HK freak-a-zoid. Only problem he stated was cost and when I checked the cost of a new select fire lower in my HK LE catalog, I was stunned. Four hundred bucks! That's my cost for a new one, so street is going to be stratospheric. Your lugged barrel has to come from the used or surp. market, because HK won't sell those. Looked over my list and saw that.
Was at the subguns advertisement last night and saw a MP5K for sale for $9000 with a sizable list of parts. Maybe a worth while venture either way.